62 THE AMPHINEURA 
corners of the pericardial cavity, run forward under the floor of 
the pericardium, and then turn outwards and backwards to run 
back to their respective apertures right and left of the anus. 
Their thin walls are lined by a ciliated epithelium, and there are 
no accessory generative organs. 
In the nervous system there are two intimately fused cerebral 
Fic. 43. 
Chaetoderma nitidulum. A, median sagittal section; B, sagittal section of the posterior 
extremity ; C, sagittal section of the anterior extremity. o, anus; br, retractor muscle of the 
branchiae ; c.g, cerebral ganglion ; d.t, digestive tract; g, gill; go, gonad ; h, heart; i, intestine ; 
k, kidney ; 1, liver; m, mouth; me, ‘‘mesothorax”’; p.c, pallial suprarectal commissure ; 7.d, 
pericardial duct ; pe, pericardium ; pe.c, pedal commissures ; pr, ‘‘ prothorax”’; 7, radula}; s.c, 
sublingual commissure. (After Wiren.), 
ganglia bearing accessory lobes. Each ganglion gives rise to two 
longitudinal nerve-cords, the ventral or pedal cord being more 
slender than the dorsal or pallial cord. In the anterior part of 
their course the pedal and pallial cords of either side run parallel 
and adjacent to one another, but in the posterior region of the 
body they are fused together, as in Paramenia, and the two pallio- 
pedal cords thus formed are united dorsad of the rectum by a 
