Nephridia sentence example

nephridia
  • In these and other Chaetopods the coelom is also put into indirect relations with the outside world by the nephridia and by the gonad ducts.
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  • The dorsal vessel also communicates with the ventral vessel indirectly by the intestinal sinus, which gives off branches to both the longitudinal trunks, and by tegementary vessels and capillaries which supply the skin and the nephridia.
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  • nephridia and coelomoducts.
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  • The nephridia, in fact, on this view, are ectodermic ingrowths, the coelomoducts coelomic outgrowths.
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  • Bergh (for Lumbricus and Criodrilus), whose figures show a derivation of the entire nephridium from mesoblast, and an absence of any connexion between successive nephridia by any continuous band, epiblastic or mesoblastic. A midway position is taken up by Wilson, who asserts the mesoblastic formation of the funnel, but also asserts the presence of a continuous band of epiblast from which certainly the terminal vesicle of the nephridium, and doubtfully the glandular part of the tube is derived.
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  • There are, however, anatomical and histological differences to be seen at any rate at the extremes between the undoubted nephridia of Goodrich, Meyer and Lankester, and the coelomoducts of the same authors.
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  • Nephridia.
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  • - Excretory organs which are undisputed nephridia are practically universal among the Oligochaeta, Hirudinea and Archiannelida, and occur in many Polychaeta.
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  • The condition is interesting as a persistence of the conditions obtaining in the provisional nephridia of e.g.
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  • Rhynchelmis, which afterwards become by an enlargement and opening up of the funnel the permanent nephridia of the adult worm.
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  • c.s, cst, f, g f, n, n.c, n.p, nst, nu, 5, to be compared with similarly-placed cells in the nephridia of Amph.ioxus.
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  • There are so many differences of detail that no line can be drawn between the one-celled funnel of Aeolosoma and the extraordinarily large and folded funnel of the posterior nephridia in the Oligochaete Thamnodrilus.
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  • This form of nephridia leads to the shorter but essentially similar organs in the Polychaete Sternaspis, and to those of the Echiuroidea (q.v.) and of the Gephyrea.
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  • Though the paired arrangement of the nephridia is the prevalent one in the Chaetopoda, there are many examples, among the Oligochaeta, of species and genera in which there are several, even many, nephridia in each segment of the body, which may or may not be connected among themselves, but have in any case separate orifices on to the exterior.
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  • There is not a great deal of difference between most of these structures and true nephridia.
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  • oviducts of Oligochaeta, sperm ducts of Phreoryctes, the coelomoducts occupy, like the nephridia, two segments, the funnel opening into that in front of the segment which carries the external pore.
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  • In the case of many Oligochaeta where there is no vascular network surrounding the nephridium, this function must be the chief one of those glands, the more elaborate process of excretion taking place in the case of nephridia surrounded by a rich plexus of blood capillaries.
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  • A consideration of the mode of development and appearance of the coelomoducts that have thus far been enumerated (with the possible exception of those of the leeches) seems to show that there is a distinct though varying relation between them and the nephridia.
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  • In the genital segments of Eudrilus the nephridia are present, but the funnels have not been found though they are obvious in other segments.
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  • Benham) the sperm ducts are hardly to be distinguished from nephridia; they are sinuous tubes with an intra-cellular duct.
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  • But the funnel is large and thus differs from the funnels of the nephridia in adjoining segments.
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  • The more complete replacements, such as the nephridia of the genital segment of Tubifex by a subsequently formed genital duct, may be compared with the succession of the nesonephros to the pronephros in vertebrates, and of the metanephros to the mesonephros in the higher vertebrates..
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  • and which have no relation whatever to nephridia or to the organs.
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  • Nephridia sometimes of the type of those of the Oligochaeta; in other cases short, wide tubes with a large funnel serving also entirely or in part as gonad ducts.
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  • The nephridia of the Polychaeta have been generally dealt with above in considering the nephridial system of the Chaetopoda as a whole.
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  • 2) is much like that of the nephridia in the Enchytraeidae.
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  • It is possible that we have here gonad ducts distinct from nephridia which at the time of sexual maturity do open on to the exterior.
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  • In Polynoe the nephridia are short tubes with a slightly folded funnel whose lumen is intercellular, and this intercellular lumen is characteristic of the Polychaetes as contrasted with leeches and Oligochaetes.
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  • The anterior nephridia, of which there are one to three pairs, contrast with the posterior series by their small funnels and large size, the posterior nephridia having a large funnel followed by a short tube.
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  • In Chaetozone setosa the anterior nephridia occupy five segments.
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  • There is usually a gap between the two series, several segments being without nephridia.
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  • It seems that the posterior nephridia are mainly gonad ducts, and the gonads are developed in close association with the funnels.
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  • The same arrangement is found in some other Polychaetes; for instance, in Sabellaria there is a single pair of large anterior nephridia, which open by a common pore, followed after an interval by large-funnelled and short nephridia.
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  • This differentiation is not, however, peculiar to the Polychaetes; for in several Oligochaetes the anterior nephridia are of large size, and opening as they do into the buccal cavity clearly play a different function to those which follow.
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  • In Thamnodrilus, as has been pointed out, there are two series of nephridia which resemble those of the Terebelloidea in the different sizes of their funnels.
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  • In Lanice conchilega the posterior series of nephridia are connected by a thick longitudinal duct, which seems to be seen in its most reduced form in Owenia, where a duct on each side runs in the epidermis, being in parts a groove, and receives one short tubular nephridium only and occupies only one segment.
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  • This connexion of successive nephridia (in Lanice) has its counterpart in Allolobophora, Lybiodrilus, and apparently in the Lumbriculids Teleuscolex and Styloscolex, among the Oligochaeta.
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  • It is noteworthy that in this family only among the Polychaeta, the nephridia are not restricted to a single pair in each segment; so that the older view that the gonad ducts are metamorphosed nephridia is not at variance with the anatomical facts which have been just stated.
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  • - " Errant" Polychaetes with well-marked prostomium possessing tentacles and palps with evident and locomotor parapodia, supported (with few exceptions) by strong spines, the aciculi; muscular pharynx usually armed with jaws; septa and nephridia regularly metameric and similar throughout body; free living and predaceous.
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  • Nephridia in two series; large, anterior nephridia followed by small, short tubes in abdomen.
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  • In other forms genital ducts and nephridia coexist in the same segment.
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  • The nephridia are sometimes numerous in each segment.
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  • The prostomium has many long filaments which recall the gills of the Sabellids, &c. The nephridia are specialized into two series, as in the last-mentioned worms. (5) Spioniformia (including Chaetopterus, Spio, &c.) and (6) Scoleciformia (Arenicola, Chloraema, Sternaspis) are the remaining groups.
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  • In both, the nephridia are all alike; there are no jaws; the prostomium rarely has processes.
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  • Nephridia generally paired, often very numerous in each segment, in the form of long, much-coiled tubes with intracellular lumen.
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  • The nephridia in this group are invariably coiled tubes with an intracellular lumen and nearly invariably open into the coelom by a funnel.
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  • They also agree in the general structure of the nephridia.
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  • It has been ascertained that the nephridia of Oligochaeta are preceded in the embryo by a pair of delicate and sinuous tubes, also found in the Hirudinea and Polychaeta, which are larval excretory organs.
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  • It is not quite certain whether these are to be regarded as the remnant of an earlier excretory system, replaced among the Oligochaeta by the subsequently developed paired structures, or whether these "head kidneys" are the first pair of nephridia precociously developed.
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  • The former view has been extensively held, and it is supported by the fact that in Octochaetus the first segment of the body has a pair of nephridia which is exactly like those which follow, and, like them, persists.
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  • On the other hand, in most Oligochaeta the first segment has in the adult no nephridium, and in the case of Octochaetus the existence of a "head kidney" antedating the subsequently developed nephridia of the first and other segments has neither been seen nor proved to be absent.
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  • In any case the nephridia which occupy the segments of the body generally are first of all represented by paired structures, the "pronephridia," in which the funnel is composed of but one cell, which is flagellate.
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  • Thus the nephridia, in this case at least, are a part of the coelom and are not shut off from it by a layer of peritoneum, as are other organs which lie in it, e.g.
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  • A growth both of the funnel, which becomes multicellular, and of the rest of the nephridium produces the adult nephridia of the genera mentioned.
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  • In the genera Pheretima, Megascolex, Dichogaster, &c., each segment contains a large number of nephridia, which, on account of the fact that they are necessarily smaller than the paired nephridia of e.g.
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  • A complex network, however, does occur in Lybiodrilus and certain other Eudrilidae, where the paired nephridia possess ducts leading to the exterior which ramify and anastomose on the thickness of the body wall.
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  • The Oligochaeta are the only Chaetopods in which undoubted nephridia may possess a relationship with the alimentary canal.
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  • Thus, in Octochaetus multiporus a large nephridium opens anteriorly into the buccal cavity, and numerous nephridia in the same worm evacuate their contents into the rectum.
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  • The anteriorly-opening and usually very large nephridia are not uncommon, and have been termed "peptonephridia."
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  • There are a clitellum and sperm ducts which though like nephridia have a larger funnel and a less complexly wound duct.
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  • Nephridia always paired and without plexus of blood capillaries.
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  • Sperm ducts and atria as in Limicolae; egg sacs large; body wall thick; vascular system and nephridia as in Terricolae.
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  • Nephridia as a rule with abundant vascular supply.
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  • Nephridia sometimes very numerous in each segment.
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  • There are no setae and apparently only two pairs of nephridia, of which the anterior pair open commonly by a common pore on the third segment after the head, whose segments have not been accurately enumerated.
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  • Nephridia always paired, rarely (Pontobdella) forming a network communicating from segment to segment; lumen of nephridia always intracellular, funnels pervious or impervious.
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  • In the middle of the body, where the limits of the somites can be checked by a comparison with the arrangement of the nephridia and the gonads, and where the ganglia are quite distinct and separated by long connectives, each ganglion is seen to consist of six masses of cells enclosed by capsules and to give off three nerves on each side.
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  • So that a leech in which only twenty-seven segments are apparent by the enumeration of the annuli, separate ganglia, nephridia, lines of sensillae upon the body, really possesses an additional seven lying behind that which is apparently the last of the series and crowded together into a minute space.
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  • The nephridia are like those of the Oligochaeta in general structure; that is to say, they consist of drain-pipe cells which are placed end to end and are perforated by their duct.
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  • In Pontobdella and Branchellion the nephridia form a network extending from segment to segment, but there is only one pair of funnels in each segment.
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  • Slight differences in form have been noted between nephridia of different segments; but the Hirudinea do not show the marked differentiation that is to be seen in some other Chaetopods; nor do the nephridia ever acquire any relations to the alimentary canal.
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  • In Acanthobdella the testes are, however, not contained in the general coelom, and the nephridia lie in the septa.
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  • These septa are, however, rather incomplete and are not fastened to the gut; and, as in Acanthobdella, the nephridia are embedded vv FIG.
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  • - Diagram of the two renal organs (nephridia), to show their relation to the rectum and to the pericardium.
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  • Such cannulated cells are characteristic of the nephridia of many worms, and the organs thus formed in the embryo Limnaeus are embryonic nephridia.
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  • Similar larval nephridia occur in other Gastropoda.
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  • n, Nephridia.
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  • Associated with the lateral blood-vessels are the single pair of nephridia.
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  • There is no communication between the nephridia on one side and the other, but in Eupolia there are ducts opening into the alimentary canal as well as to the exterior, a condition of things which recalls what obtains in certain Oligochaetes.
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  • In Stichostemma, however, Montgomery 1 has described a series of nephridia lying all along the body, and each with a varying number of external pores.
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  • The two external openings of the nephridia are situated sometimes more 2 towards the ventral, at other times more towards the dorsal side.
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  • In transverse sections the nephridia can be shown to be generally situated in the region limited by (I) the proboscidian sheath, (2) the upper wall of the intestine, (3) the muscular body-wall.
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  • No trace of nephridia is found posterior to the oesophagus.
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  • the nephridia or excretory 14.
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  • The kidneys or nephridia open internally by wide funnel-shaped nephridiostomes and externally by small pores on each side of the mouth near the base of the arms. Each is short, gently curved and devoid of convolutions.
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  • The structures formerly regarded as pseudohearts have been shown by Huxley to be nephridia; the true heart was described and figured by A.
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  • The dorsal branch sends a blind twig into each of the diverticula of the dorsal mantle-sinus, the ventral branch supplies the nephridia and neighbouring parts before reaching the ventral lobe of the mantle.
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  • through the nephridia.
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  • these the nephridia open.
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  • The cloaca is often very large; the nephridia and oviducts may open into it, and the eggs lodge there on their way outwards; they are thrown out, as are the faecal masses, by an eversion of the cloaca.
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  • The nephridia (fig.
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  • B, lateral view, showing viscera: oc, eye-spots; n, nephridia; e, ciliated toes; other letters as above.
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  • As in Cephalopoda (and possibly other Mollusca) water can be introduced through the nephridia into this space.
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  • (6) Diagram to show the positions of the nerve-ganglia, heart and nephridia.
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  • Floor of the pericardium separating that space from the non-glandular portion of the nephridia.
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  • - Diagrams showing the Relations of Pericardium and Nephridia in a Lamellibranch such as Anodonta.
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  • The blood makes its way by large veins to a venous sinus which lies in the middle line below the heart, having the paired renal organs (nephridia) placed between it and that organ.
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  • Hence it passes through the vessels of the glandular walls of the nephridia right and left into the gilllamellae, whence it returns through many openings into the widelystretched auricles.
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  • Previously to Hoek's discovery a brown-coloured investment of the auricles of the heart of the oyster had been supposed to represent the nephridia in a rudimentary state.
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  • True nephridia do not primarily open into the coelom, as was formerly taught, but are intra-cellular ducts in the mesoderm.
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  • Such organs are absent in Mollusca in the adult state, but a pair of nephridia usually occurs in the larva.
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  • In animals which exhibit typical segmentation or metamerism, such as segmented worms (Chaetopoda), each segment or metamere possesses its own coelomic cavity, a pair of coelomic ducts, and a pair of nephridia.
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  • The structure of the Mollusca in the greater number of cases agrees with the hypothesis that the primitive form was unsegmented, and therefore had but one pair of coelomic ducts and one pair of nephridia.
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  • In the Dibranchia true nephridia have not been detected in the embryo, nor has it been shown that the genital ducts are derived from the renal tubes.
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  • On the whole, then, the most probable conclusion is that the original ancestral form of the Mollusca was unsegmented, possessed one pair of true nephridia, and one pair of coelomic ducts whose function was to conduct the generative products to the exterior.
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  • In the larvae of several Gastropoda and Lamellibranchia occur excretory organs which have the characters of true nephridia.
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  • They agree with primitive nephridia in being of ectodermic origin, in consisting of perforated cells in linear series, and in having no communication with the coelom.
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  • They invariably disappear before the adult stage is reached, but their presence in the larva is evidence that the ancestral mollusc possessed a pair of true nephridia quite distinct from the coelomic excretory organs, which are so characteristic of existing forms in the adult condition.
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  • - Dissection of the renal organs (nephridia) of Chiton siculus.
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  • In this case there should be only one pair of coelomoducts in the adult, the pair of true nephridia which should also occur being represented by the larval nephridia.
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  • The body is composed of a large number of segments; the prostomium bears a pair of tentacles; the nervous system consists of a brain and longitudinal ventral nerve cords closely connected with the epidermis (without distinct ganglia), widely separated in Saccocirrus, closely approximated in Protodrilus, fused together in Polygordius; the coelom is well developed, the septa are distinct, and the dorsal and ventral longitudinal mesenteries are complete; the nephridia are simple, and open into the coelom.
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  • In the male there are a right and a left protrusible penis in every genital segment, into which opens the nephridium and a sperm-sac. The wide funnels of the nephridia of this region are possibly of coelomic origin.
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  • It resembles Dinophilus in the possession of a ventral pharyngeal pouch (which bears teeth in Histriodrilus only), the small number of segments, and absence of distinct septa, the absence of a vascular system, the presence of distinct ganglia on the ventral nerve cords, and of small nephridia which do not appear to open internally.
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  • The excretory organs are typical nephridia, with an internal ciliated opening into the body-cavity, and an external pore.
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  • These tubules are the excretory tubules or nephridia.
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  • Into this same cloacal chamber open ventrally a pair of ciliated tubes communicating by funnels with the coelom (Nansen and Wheeler); these are possibly nephridia, and excretory in function.
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  • as pairs in each ring-like segment or somite of the body, and some of these are in all cases retained as gonoducts and often as renal excretory organs (green glands, coxal glands of Arachnida, not crural glands, which are epidermal in origin); but true nephridia, genetically identical with the nephridia of earthworms, do not occur (on the subject of coelom, coelomoducts and nephridia, see the introductory chapter of part ii.
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  • The reproductive cells pass to the exterior by means of the nephridia.
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  • It contains two tufts of peculiar excretory cells, described by Goodrich (5) as " solenocytes," which surround the blind ends of a pair of nephridia.
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  • The supposed occurrence of a pair of nephridia in certain Phylactolaemata, in a position corresponding with that of the nephridia of Phoronis, must also be mentioned, although it has been maintained that the "nephridia " of Phylactolaemata are merely ciliated portions of the body-cavity and not indeed nephridia at all.
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  • The legs of the fourth and fifth pairs differ from the others in the fact that the third pad (counting from the distal end of the leg) carries the opening of the enlarged nephridia of these segments.
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  • Nephridia are present in all the legs.
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  • The nephridia of the first three pairs of legs are smaller than the rest, consisting only of a vesicle and duct.
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  • The external opening of the other nephridia is placed at the outer end of a transverse groove at the base of the legs.
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  • The salivary glands are the modified nephridia of the segment of the oral papillae.
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  • There appear to be present in most, if not all, of the legs some accessory glandular structures opening just externally to the nephridia.
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  • The jaw somite also disappears; the oral papilla somite forms ventrally the salivary glands, which are thus serially homologous with nephridia.
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  • The Annelidan features are: (I) the paired nephridia in every segment of the body behind the first two (Saenger, Balfour); (2) the presence of cilia in the generative tracts (Gaffron).
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  • Segmentally arranged paired nephridia are present.
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  • Body cavity is continuous with the vascular system, and does not communicate with the paired nephridia.
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  • In its earlier conception, this view embraced as homologous organs (so far as the present group is concerned) not only the nephridia of Oligochaeta and Hirudinea, which are obviously closely similar, but the wide tubes with an intercellular lumen and large funnels of certain Polychaeta, and (though with less assurance) the gonad ducts in Oligochaeta and Hirudinea.
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  • It is therefore by no means certain that so profound a difference embryologically can be asserted to exist between the excretory nephridia and the ducts leading from the coelom to the exterior, which are usually associated with the extrusion of the genital products among the Chaetopoda.
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  • In the lastmentioned worm the funnels of the anterior nephridia are small and but few celled; it is only the nephridia in and behind the 17th segment of the body which are particularly large and with a sinuous margin, which recall the funnels of the gonad ducts (i.e.
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  • In this category are included (by Goodrich and Lankester) the gonad ducts of the Oligochaeta, certain funnels without any aperture to the exterior that have been detected in Nereis, &c., funnels with wide and short ducts attached to nephridia in other Polychaeta, gonad ducts in the Capitellidae, the gonad ducts of the leeches.
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  • The gonad ducts of Lumbricus, &c., must perform one function of nephridia; they must convey to the exterior some of the coelomic fluid with its disintegrated products of waste.
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  • It has been shown that in Tubifex, and some other aquatic Oligochaeta, the genital segments are at first provided with nephridia, and that these disappear on the appearance of the generative ducts, which are coelomoducts.
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  • It might be well to term these structures, mostly serving as gonad ducts, which have an undoubted resemblance to nephridia, and for the most part an undoubted connexion with nephridia, "Nephro dinia," to distinguish them from another category of "ducts" which are communications between the coelom and the exterior,.
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  • On the hypothesis that such a form as Dinophilus (see Haplodrili) has preserved the characters of the primitive Chaetopod more nearly than a any existing Polychaet or Oligochaet, it is clear that the nephridia in the Oligochaeta have preserved the original features of those organs more nearly than most Polychaeta.
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  • In this worm the paired nephridia exist in most of the segments of the body, and their form (see fig.
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  • Among the Capitellidae, which in several respects resemble the Oligochaeta, wide and short gonad ducts coexist in the same segments with nephridia, the latter being narrower and longer.
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  • There are no renal organs with a wide intercellular lumen, such as occur in the Polychaeta, nor is there ever any permanent association between nephridia and ducts connected with the evacuation of the generative products, such as occur in Alciope, Saccocirrus, &c. In these points the Oligochaeta agree with the Hirudinea.
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  • These structures appear to be absolutely distinctive of the Oligochaeta, unless the sacs which contain sperm and open in common with the nephridia of Saccocirrus (see Haplodrili) are similar.
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  • They have till recently been very generally identified with the nephridia of Chaetopod worms, but there is good reason for considering the true nephridia (typified by the nephridia of the earthworm) as a distinct class of organs (see Lankester in vol.
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  • They possess a modified anterior end, frequently with special sense organs, forming a head, a segmented nervous system, consisting of a pair of anterior, dorsally-placed ganglia, a ring surrounding the A ? ??° D B L/ alimentary canal, and a double ventral ganglionated chain, a definite vascular system, an excretory system consisting of nephridia, and paired generative organs formed from the coelomic epithelium.
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