GONIODORIS. 



that of Boris. In G. castanea the vaginal tube is very much shorter than in G. nodosa, and 

 can scarcely be said to be doubled upon itself; the large spermatheca is elliptical, and is also 

 much smaller than in the other species. 



The vascular and respiratory system, so far as we have been able to ascertain, are in the 

 same condition as in Boris. The heart rests on the upper surface of the liver, and is contained 

 in a well-defined pericardium (q). The auricle (s), receives the blood by two lateral vessels 

 (t, t), from the skin, and by a posterior median one («), from the gills ; that is, in this way it 

 is returned from the general system and from the liver mass : it is then passed into the 

 ventricle (r), and is distributed to the various organs by arteries, which branch from a large 

 trunk that issues, in the usual manner, from the anterior apex of the propelling organ. The 

 portal heart (w), is distinctly seen lying below the pericardium, into which it opens, and its 

 vascular trunk can be traced into the renal organ. From these facts, it is evident that here, 

 as in Boris, the blood is returned to the heart only partially aerated, and that the systemic 

 circulation is twofold, — general and partial ; the latter comprising a portal circulation. 



The renal organ {y) covers the greater portion of the upper surface of the liver, lying 

 immediately above the ovary, and resembles the same organ in Boris pilosa. Its margins are 

 somewhat sinuous, and the inner surface of the circumscribing membrane is richly supplied 

 with a vascular net-work, with which the twigs from the trunk given off by the portal heart 

 go to inosculate. The renal orifice opens externally, close to the base of the anal nipple, in 

 front and to the right side. 



The nervous system is highly concentrated in this genus. There are four principal 

 oesophageal ganglia, and four buccal ; of the former, two are above, and two at the side of the 

 alimentary tube ; those above are broadly ovate, with their sharper ends placed towards the 

 median line, across which they are united. These ganglionic masses (fig. 4 a, a) are 

 composed of the cerebroid and branchial ganglia, completely fused ; and give off, from the 

 upper surface of the frontal margin two large nerves (1), which go to the dorsal tentacles: 

 these have attached to them, at their origin, the olfactory ganglia {c, c), which are round, and 

 almost as large as the buccal ganglia. Three other pairs of nerves (2, 3, 4) pass from the 

 under surface in front, and go to the channel of the mouth and lips ; the largest of these (3) 

 gives a stout branch to the oral tentacles. From behind, — the branchial portion, — a larger 

 nerve (6) is given off from each mass, and goes to supply the dorsal skin or mantle. 



The pedial or lateral ganglia (6, 6) are closely united to the under surface of the upper 

 pair, and are joined below the oesophagus by a short, stout, commissural cord (y), the great 

 oesophageal collar, composed of two filaments — one being much finer than the other. These 

 ganglia furnish each two or three nerves to the foot. 



A small visceral ganglion (d) is attached to the under surface of the right upper 

 ganglionic mass behind ; consequently to the branchial portion of it. It gives off two or 

 three nerves (11, 12), which go to the viscera. A commissural cord (*), also comes off from this 

 ganglion, and passing under the alimentary tube, in conjunction with the great oesophageal or 

 pedial collar, goes to the branchial portion of the opposite ganglion. There is also another 

 nerve from the oesophageal ganglia ; this (7) comes from the right upper ganglion, close to 

 the visceral, and may possibly belong to it. This nerve goes to one or two small ganglia (j), 

 on the root of the penis. 



The eyes, which are as well developed as in Boris, are fixed on small roundish ganglia 



