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 Nuttalochiton, 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 
Fie. 29; 
Renal organs ot Boreochiton cinereus, 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 ; Il, mantle; III, external ramifications of the 
antero-posterior (or terminal) renal part ; [V, 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 ITI ; 
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. 
