In this use the term loses, of course, its morphoI logical value, and it is better to call such a segment of a broken-up I stele a meristele, the whole solenostele with overlapping leaf-gaps being called a dictyostele.
Probably due to a folding of the segment by which the two halves come to lie more or less parallel to each other, and form variously shaped figures of greater or less regularity (fig.
The Curculionidae, or weevils (q.v.), comprising 23,000 species, are by far the largest family of the group. The maxillary palps are short and rigid, and there is no distinct labrum, while the feelers are usually of an "elbowed" form, the basal segment being very elongate (figs.
- The head of an ant carries a pair of elbowed feelers, each consisting of a minute basal and an elongate second segment, forming the stalk or " scape," while from eight to eleven short segments make up the terminal " flagellum."
This remark applies to the finding of the area of a parabolic segment (mechanical solution) and of a spiral, the surface and volume of a sphere and of a segment thereof, and the volume of any segments of the solids of revolution of the second degree.
The first book contains forty-four propositions, and those in which the most important results are finally obtained are: 13 (surface of right cylinder), 14, 15 (surface of right cone), 33 (surface of sphere), 34 (volume of sphere and its relation to that of circumscribing cylinder), 42, 43 (surface of segment of sphere), 44 (volume of sector of sphere).
3, 4), and of constructing a segment of a sphere similar to one given segment and having (a) its volume, (b) its surface, equal to that of another (5, 6).
The second book in ten propositions is devoted to the finding the centres of gravity (I) of a parabolic segment, (2) of the area included between any two parallel chords and the portions of the curve intercepted by them.
(6) The Quadrature of the Parabola (Tetragonismos paraboles) is a book in twenty-four propositions, containing two demonstrations that the area of any segment of a parabola is a of the triangle which has the same base as the segment and equal height.
(7) On Floating Bodies (Peri okoumenon) is a treatise in two books, the first of which establishes the general principles of hydrostatics, and the second discusses with the greatest completeness the positions of rest and stability of a right segment of a paraboloid of revolution floating in a fluid.
Turning to the thorax we find that the first segment (prothorax) is distinct and free, with a wide dorsal sclerite.
But the legs carry peculiar spines, and the terminal tarsal segment is cup-shaped at the end; from this hollow a delicate bladder (fig.
The young insect resembles its parent in most points, but the head is disproportionately large; the anterior abdominal spiracles are on the second segment instead of on the first, and the foot has only a single segment.
I, 4) the abdomen is cylindrical, the female is provided with a ventral ovipositor and has the terminal abdominal segment conical; the corresponding segment in the male is usually bluntly rounded.
These insects have the abdomen flattened, with its terminal segment (see fig.
R, Optical section of leptoid (sieve-tube segment) of Phanerogam, with two proteid (companion) cells.
This consists of a few xylem elements, e a a segment of phloem, pericycle, and usually an arc of h~s endodermis, which closes round the bundle as it detaches ~
In the latter case each segment of the solenostele frequently resembles a Dktyosteb.
Apical cell, p. Wall marking limit between the plerome k, initial segment of root-cap. P and the pleriblem Pb.
A tissue mother-cell of the xylem may, in the most advanced types of Dicotyledons, give rise to(I) a tracheid; (2) a segment of a vessel; (3) a xylem-fibre; or (4) a vertical file of xylem-parenchyma cells.
A tissue mother-cell of the phloem may give rise to (i) a segment of a sieve-tube with its companion cell or cells; (2) a phloem fibre; (3) a single phloem-parenchyma (cambiform) cell, or a ve~rtical file of short parenchyma cells.
Some observers consider that it represents a longitudinal half of the original segment of the spireme, others that it is a half of the segment produced by transverse division by means of which a true qualitative separation of the chromatin is brought about.
The female can protrude a long flexible tube in connexion with the eighth segment, carrying the sclerites of the ninth at its extremity, and these sclerites may carry short hairy processes A B D.yrnt,sc/'rle moathd ..
In male beetles, however, the two pairs of genital processes (paramera) belonging to the ninth abdominal segment are always present, though sometimes reduced.
2 c) are active, with well-chitinized cuticle, often with elongate tail-feelers (cerci), and with five-segmented legs, the foot-segment carrying two claws.
The fifth abdominal segment has a pair of strong dorsal hook-like processes, by means of which the larva supports itself in the burrow which it excavates in the earth, the great head blocking the entrance with the mandibles ready to seize on any unwary insect that may venture within reach.
Antennal segment s form a distinct club.
- The Rhynchophora are a group of beetles easily recognized by the elongation of the head into a beak or snout, which carries the feelers at its sides and the jaws at its tip. The third tarsal segment is broad and bi-lobed, and the fourth is so small that the feet seem to be only four-segmented.
39) have jointed, flexible palps, feelers - often of excessive length - with a short basal segment, and the three terminal segments forming a club, and, in some genera, larvae with legs.
The insects of this order have mandibles adapted for biting, and two pairs of membranous wings are usually present; the first abdominal segment (propodeum) becomes closely associated with the fore-body (thorax), of which it appears to form a part.
In all ants the second (apparently the first) abdominal segment is very markedly constricted at its front and hind edges, so that it forms a "node " at the base of the hind-body (fig.
The fourth abdominal segment is often very large, and forms the greater part of the hind-body; this segment is markedly constricted at its basal (forward) end, where it is embraced by the small third segment.
In many of those ants whose third abdominal segment forms a second " node," the basal dorsal region of the fourth segment is traversed by a large number of very fine transverse striations; over these the sharp hinder edge of the third segment can be scraped to and fro, and the result is a stridulating organ which gives rise to a note of very high pitch.
In these ants the difference between the large, heavy, winged males and females, and the small, long-legged, active workers, is so great, that various forms of the same species have been often referred to distinct genera; in Eciton, for example, the female has a single petiolate abdominal segment, the worker two.
Biisgen that the sweet secretion (honey-dew) of the aphids is not derived, as generally believed, from the paired cornicles on the fifth abdominal segment, but from the intestine, whence it exudes in drops and is swallowed by the ants.
Fielde show that an ant follows her own old track by a scent exercised by the tenth segment of the feeler, recognizes other inmates of her nest by a sense of smell resident in the eleventh segment, is guided to the eggs, maggots and pupae, which she has to tend, by sensation through the eighth and ninth segments, and appreciates the general smell of the nest itself by means of organs in the twelfth segment.
Commonly the nephridia are strictly paired a single pair to each segment, while the branches of the blood vascular system are similarly metameric. The alimentary canal is nearly always a straight tube running from the mouth, which is surrounded by the first segment of the body and overhung by the prostomium, to the anus,which is then either surrounded by the last segment of the body or opens dorsally a little way in front of this.
It is, however, always possible to recognize a head, which consists at least of the peristomial segment with a forward projection of the same, the prostomium.
The prostomium overhangs the mouth, and is often of considerable size and, as a rule, quite distinct from the segment following, being A„ f s / 6/ ' A B I.
On the other hand, in certain Polychaeta the bundles of setae are so extensive that they nearly form a complete circle surrounding the body; and in the Oligochaet genus Perichaeta (=Pheretima), and some allies, there is actually a complete circle of setae in each segment broken only by minute gaps, one dorsal, the other ventral.
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.
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.
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.
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..
As in the Oligochaeta the peristomial segment is often without setae; but this character is not by any means so constant as in the Oligochaeta.
The funnel, which is not large, appears to open, as a rule at least, into the segment in front of that which bears the external orifice.
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.
The genital ducts are limited to one segment (the 8th in Capitella capitata), and there are genital setae on this and the next FIG.
Setae very rarely absent (genus Achaeta) and as a rule not so large or so numerous in e (.r, each segment as in the is Polychaeta, and different in shape.
In terrestrial A, Lumbricus : 9, to, segments contain ing spermathecae, the orifices of forms dorsal pores are usuwhich are indicated; 14, segment b ally present; in aquatic earing oviducal pores; 15, segforms a head pore only.
Nephridia generally paired, often very numerous in each segment, in the form of long, much-coiled tubes with intracellular lumen.
When present they are either arranged in four bundles of from one to ten or even more setae, or are disposed in continuous lines completely encircling each segment of the body.
It has been shown (Bourne) that the "perichaetous" condition is probably secondary, inasmuch as in worms which are, when adult, "perichaetous" the setae develop in pairs so that the embryo passes through a stage in which it has four bundles of setae, two to each bundle, the prevalent condition in the group. Rarely there is an irregular disposition of the setae which are not paired, though the total number is eight to a segment (fig.
- Diagrams of various Earth of several Geoscolicidae, the nephridiopores indicate the segments; to each segment corresponds internally a chamber of the coelom which is separated from adjacent segments by transverse septa,which are only unrecognizable in the genus Aeolosoma and in the head region of other Oligochaeta.
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.
Some were thickly set with glittering teeth resembling ivory saws; others were tufted with knots of human hair; and one was sickle-shaped, with a vast handle sweeping round like the segment made in the new-mown grass by a long-armed mower.
It is a little star-dust caught, a segment of the rainbow which I have clutched.
It's a one-week tour, each day a separate segment, with everyone riding at their own pace—within reason.
While it is not improbable that the collar-pores and the proboscispores may evacuate excretory substances, there can be little doubt that their primary function is to regulate the turgidity of the segment to which they respectively belong.
The general graphy, principle Arms a and arrangement b, one at eachstation and d B, are connected to the line wire, and are made to rotate simultaneously over metallic segments, 3, 4, and I', 3', 4', at the two stations, so that when the arm a is on segment i at A, then b is on segment I' at B, and so on.
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.
Zoned by those letters you saw the likeness of three Andes' summits; from one a flame; a tower on another; on the third a crowing cock; while arching over all was a segment of the partitioned zodiac, the signs all marked with their usual cabalistics, and the keystone sun entering the equinoctial point at Libra.
In forehand play the bowl as it courses to the jack describes its segment of a circle on the right, in backhand play on the left.
C, Nuclear thread segment ing.
The ventral region of the thoracic skeleton is complex, each segment usually possessing a median sternum with paired episterna (in front) and epimera (behind).
I), and in many ants the third abdominal segment is similarly " nodular " in form (fig.
The setae, which are always absent from the peristomial segment, are also sometimes absent from a greater number of the FIG.
Otherwise be limited to a half segment of a circle. The regions thus
The conversion of the gravel road into a paved road made it much easier for riding bikes.