THE AMPHINEURA 



47 



generally correlated with that of the branchial row. The two 

 branches of the renal canal may be fused together from before 

 backwards until, as in Callistochiton and Nuttakchiton, the kidney 

 has the form of a simple sac with more or less numerous 

 arborescent appendages, and the pericardial and external apertures 

 adjacent to one another at its hinder end. A similar form of 

 specialisation may be seen in the kidneys of Lamellibranchs. The 

 renal canal may be complicated by the addition of two accessory 



FIG. 20. 



Renal .organs of Boreovhiton cinereiis, dorsal aspect ; on the right-hand side, the exterior 

 ramifications of the antero-posterior renal part are alone drawn ; on the left-hand side, all the 

 other ramifications are drawn. I, pedal cord ; II, mantle ; III, external ramifications of the 

 antero-posterior (or terminal) renal part ; IV, reno-pericardial orifice ; V, posterior point of the 

 urinary chamber; VI, external renal pore; VII, urinary chamber; VIII, postero-anterior (or 

 initial) portion of the kidney; IX, antero-posterior (or terminal) portion of the kidney; X, 

 internal ramifications of the antero-posterior portion of the kidney ; XI, left outer limit of III ; 

 XII, ramifications of the initial portion of the kidney ; 1-8, the eight "segments" of the body. 



longitudinal branches, an anterior larger and a posterior smaller, 

 which lie in the foot near the middle of the body. 



4. Nervous System and Sense-organs. There is no concentration 

 of nerve-ganglion cells to form distinct ganglia, but the larger nerve- 

 cords are ganglionic throughout their extent. There are two 

 pairs of longitudinal nerve-cords, united in front of the buccal 

 mass by a supra -oesophageal or cerebral commissure. Ganglionic 

 enlargements on this commissure are found only in Callochiton 

 doriae. 



