Tes MORPHOLOGY OF THE MOLEUSCA. 5 
enlargements of this nerve-ring is a pair of ventral or pedal 
cords, connected with one another by a series of commis- 
sures lying beneath the gut, and also with the lateral cords 
by means of lateral connectives. The lateral cords inner- 
vate the pallial sense-organs, gills, and viscera; the ventral 
cords the musculature of the foot. The lateral cords are 
regarded by Thiele as the homologues of the lateral cords 
or nerve-ring of the Turbellarians, and the ventral cords are 
taken to correspond to the ventral longitudinal nerves of 
the same forms. So far we find nothing either erratic or 
original, for the same view has already been taken by Lang 
(16). 
But the novelties begin with Thiele’s interpretations of 
the nervous system of Gastropoda and Pelecypoda. We 
have already pointed out Thiele’s view that the epipodium 
of Gastropods represents the primitive body-edge. Now 
at the base of the epipodium in /7ssurella and Hlaliotis there 
lies a ganglionic plexus ; and this plexus, which takes the 
form of an incomplete ring, is regarded as the homologue 
of the lateral cords of Turbellariansand Amphineura. The 
series of epipodial nerves which connect the epipodial plexus 
with the upper half of the pedal cords in Rhipidoglossa is 
compared with the series of connectives between the lateral 
and ventral cords in Amphineura. 
This seems very plausible until one recollects (1) that, 
the epipodium being infra-rectal, the epipodial plexus is 
also infra-rectal and thus difficult to compare with the 
lateral cords of Amphineura, whose ‘‘commissure” is supra- 
rectal; and (2) that, whereas in Amphineura the lateral 
cords innervate practically the whole of the pallium and 
viscera, in Rhipidoglossa the epipodial plexus has nothing 
to do with any other organs except the sense-organs of the 
epipodium. If the pallium of the Gastropoda is really, as 
Thiele maintains, a secondary differentiation of the primary 
pallium of the Amphineura, one would expect that its 
innervation would also be effected by progressive differen- 
