The fixing of stoves of this kind entails the laying of pipes or ducts from the open to convey fresh air to the back of the stove.
Lastly, to pass over unnecessary details, the markings of various kinds to be observed on the lobes of the livers of freshly-slaughtered animals, which are due mainly to the traces left by the subsidiary hepatic ducts and hepatic veins on the liver surface, were described as "holes," "paths," "clubs" and the like.
When a number of cables follow the same route, they are generally laid in conduits made up of earthenware or cement ducts; iron pipes are used when the number of cables is small.
Manholes are placed at intervals in the line of ducts to facilitate the drawing in and jointing of the cables, and surface boxes are placed in the footways for distributing purposes.
Sometimes the amber retains the form of drops and stalactites, just as it exuded from the ducts and receptacles of the injured trees.
In some cases special secreting tissues, resin ducts, oil glands, laticiferous tissue, crystal sacs, &c., may be developed among the ordinary secondary vascular elements.
The next chamber, the urodaeum, is small, and receives in its dorso-lateral wall the ureters and the genital ducts; above and below this chamber is closed by circular folds, the lower of which, towards the ventral side, passes into the coating of the copulatory organ when such is present.
It is easy to distinguish the great primitive watercourses from the lateral ducts which they fed, the latter being almost without banks and merely traceable by the winding curves of the layers of alluvium in the bed, while the former are hedged in by high banks of mud, heaped up during centuries of dredging.
The glands occur in groups, and lead into common ducts which open usually so much reduced that the foremost apparent ventral sclerite of the abdomen represents the third sternite.
Finally, he saw the spores accumulate within the cells of the salivary glands, and discovered that they actually passed down the salivary ducts and along the grooved hypopharynx into the seat of puncture, thus causing infection in a fresh vertebrate host" (Sambon).
We can hardly any longer hesitate to recognize in this vast building, with its winding corridors and subterranean ducts, the Labyrinth of later tradition; and as a matter of fact a maze pattern recalling the conventional representation of the Labyrinth in Greek art actually formed the decoration of one of the corridors of the palace.
The function of nitrogenous excretion was not therefore a necessary part of the view - though it may be pointed out that there are grounds for believing that the gonad ducts are to some extent also organs of excretion (see below).
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.
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.
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.
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 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.
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.
In Lumbricus the connexion is a little closer; the funnel of the nephridium, in the segments in which the funnels of the gonad ducts are to be developed, persists and is continuous with the gonad duct funnels on their first appearance.
Benham) the sperm ducts are hardly to be distinguished from nephridia; they are sinuous tubes with an intra-cellular duct.
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,.
In many, perhaps most, genera of the Oligochaeta family, Eudrilidae, and possibly the gonad ducts in the Hirudinea.
To this category will belong the oviducts in Teleostean fishes and probably the gonad ducts in several groups of invertebrates.
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.
It seems that the posterior nephridia are mainly gonad ducts, and the gonads are developed in close association with the funnels.
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.
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.
In other forms genital ducts and nephridia coexist in the same segment.
Special gonad ducts always present.
Male ducts often open on to exterior through a terminal chamber which is variously specialized, and sometimes with a penis.
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.
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.
These cavities communicate with the exterior through the gonad ducts, which have nothing to do with them, but whose coelomic funnels are taken up by them in the course of their growth.
The gonad ducts are male and female, and open opposite to or, rarely, alongside of the gonads, whose products they convey to the exterior.
The sperm ducts are usually longer than the oviducts; but in Limicolae both series of tubes opening by the funnel into one segment and on to the exterior in the following segment.
While the oviducts always open directly on to the exterior, it is the rule for the sperm ducts to open on to the exterior near to or through certain terminal chambers, which have been variously termed atrium and prostate, or spermiducal gland.
There are a clitellum and sperm ducts which though like nephridia have a larger funnel and a less complexly wound duct.
Spermatheca rarely with diverticula; sperm ducts as a rule occupying two segments only, usually opening by means of an atrium.
Sperm ducts and atria as in Limicolae; egg sacs large; body wall thick; vascular system and nephridia as in Terricolae.
Sperm ducts traverse several segments on their way to exterior.
The intervening segments contain the genitalia, which are on the Oligochaeta plan in that the gonads are independent of their ducts and that there are special spermathecae, one pair.
The male ducts are either one pair or two pairs, which open by a common and complicated efferent terminal apparatus furnished with a protrusible penis.
Testes several pairs, rarely one pair, continuous with sperm ducts; ovaries, one pair, continuous with oviducts; generative pores single and median.
The gonads and their ducts in the Hirudinea invariably form a closed system of cavities entirely shut off from the coelom in which they lie.
The efferent ducts are ciliated, and there is a patch of cilia at the point where they communicate with the cavity of each testis.
The two ducts continuous with the gonads open by a common vagina on to the exterior behind the male pores.
These ducts therefore have not their exact counterparts in the Oligochaeta, unless we are to assume that they collectively are represented by the seminal vesicles of earthworms and the vasa deferentia.
Two pairs of salivary ducts, each leading from a salivary gland, open into the buccal chamber.
The liver opens by two ducts into the digestive FIG.