(iii.) The collar is produced dorsally into arms (one pair in Rhabdopleura, four to eight pairs in Cephalodiscus), each of which bears numerous ciliated tentacles, the organs by which the microscopic food-particles are conveyed to the mouth.
2, nch.), growing forwards in the septum between the proboscis-cavity and the collar-cavities, and supported dorsally by the median mesentery of the collar, is the representative of the so-called notochord or stomochord of Balanoglossus; and if the view that this organ is really a notochord is well founded, it may be regarded as the homologue of the anterior end of the Vertebrate notochord.
2, 3, ov.) lie in the met asomatic cavities, and open to the exterior dorsally by short, highly pigmented oviducts (fig.
It receives the three great venous trunks of the body, namely the vena cava superior dextra, the vena cava superior sinistra more dorsally, and the vena cava inferior more to the right and below; the opening of the last is guarded by two prominent valves in place of the mammalian valvula Eustachii.
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.
Quite independent of these are certain large dorsally situate funnel-like folds of the coelomic epithelium, ciliated, but of which no duct has been discovered leading to the exterior.
In the larva a nautiloid shell is developed which is coiled exogastrically, that is, dorsally, and the pallial cavity is posterior or ventral (fig.
The detorted visceral commissure shows a tendency to the concentration of all its elements round the oesophagus, so that except in the Bullomorpha and in Aplysia the whole nervous system is aggregated in the cephalic region, either dorsally or ventrally.
Wheeler, the amnion is ruptured and turned back from covering the germ band, enclosing the yolk dorsally and becoming finally absorbed, as the ectoderm of the germ band itself spreads to form the dorsal wall.
Kaiser has described as kidneys two organs something like minute shrubs situated dorsally to the generative ducts into which they open.
The coelom then is a spacious chamber surrounding the alimentary canal, and is continued dorsally and ventrally into the sinuses of the mantle (fig.
The mouth, which is quite devoid of armature, leads imperceptibly into a short and dorsally directed oesophagus.
Which connect it with the IX, The second mesosomatic somite body-wall, both dorsally and or pectiniferous somite.
Opisthosoma was movably articulated to the prosoma, and consisted of from eight to ten segments furnished with movable lateral plates, the anal segment being overlapped dorsally by a laminate expansion of the preceding segment.
- Opisthosoma consisting of ten segments defined by integumental grooves, each of the anterior four of these furnished with a single pair of dorsally-placed spiracles or tracheal stigmata.
4 B, v), but the two apertures may run into one, and may also open dorsally (Hexacotyle).
The nervous system consists of a ganglion or brain, which lies dorsally about the level of the junction of the pharynx and the stomach, a nerve ring and a segmented neutral cord.
In the adult there is a pair of such glands opening ventrally on the hindmost thoracic segment, or at the base of the abdomen; but in the young insect the glands are situated dorsally and open to the exterior on a variable number of the abdominal terga.
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.
A, Pericardium opened dorsally a, Ventricle of the heart.
The mesoblast multiplies its cells, which become partly muscular and partly skeleto-trophic. Centro-dorsally now appears the embyronic shell-gland.
- One row of branchial filaments is directed dorsally, the other ventrally; the mantle has a long posteroventral suture and a single posterior aperture; the labial palps of each side are fused together; shell elongate; hinge without teeth; periostracum thick.
External gill-plate directed dorsally and without reflected lamella.
A pair of eyes lie dorsally and behind them is a b closed circlet, often pulled out into various shapes, of modified epidermis, to which an olfactory function has been attributed.
Dorsally the posterior nares open into this cavity.
The pharynx projects freely into the atrium; it is surrounded at the sides and below by the continuous atrial cavity, but dorsally it is held in position in two ways.
To) are set, one dorsally and one on each side.
At the base of the head dorsally are a pair of flat tentacular lobes from the edges of which the cephalic filaments or captacula arise.
Foot conical with a laterally expanded and dorsally interrupted circular fold.