62 Nils Hj. Odhner. 
and which have a similar position in Chitonellus just above the 
grooves on each side of the foot and outside the pedal cords, 
would lie, just as in Chitonellus, immediately above and outside 
the grooves, while the pedal cords would have a position inside 
them. But a quite different arrangement is observable in the Soleno- 
gastres, a disposition which agrees chiefly with that of the typical 
Chiton and completely repeats that of its larval stage. That is 
to say: the pedal cords run far remote outside the furrow and the 
lateral ones at about halfway the height of each lateral side. 
On these grounds we are unable to accept the theory generally 
current that the ventral furrow of the Solenogastres is homologous 
' with the peripedal groove of the Chitonidae, and that the fold is 
the homolgon of their toot. The fact that in some Solenogastres, 
for instance Gymnomenia, the whole ventral side is flattened makes 
it much more probable that the whole of this side represents the foot * 
sole of Chiton and other Mollusca. 
If this view is not accepted, and if the fold is nevertheless con- 
sidered to be homologous with the foot, there meet difficulties in 
establishing the agreement in the course of the muscles in a Chiton 
or a Chitonellus on the one hand, and a Solenogastre on the other. 
At the first glance at a tranverse section, one is indeed tempted 
to admit a rather close similarity in this respect. But an attempt to 
homologise the different portions of the musculature of a Chiton 
with that of a Solenogastre does not yield any satisfactory result, 
if we start from the above assumption. From the opposite point 
of view, however, we arrive at the conclusion that the ventral longi- 
tudinal muscle fascicles of the Solenogastres (Neomeniina) are the 
nearest correspondance with the Chiton foot. But in this case we 
meet with the difficulty presented by the fact that the longitudinal 
muscles in the foot of Chiton are very slightly developed, whereas, 
on the contrary, the dorso-ventral ones predominate. 
A solution of these difficulties is however afforded, if we consi- 
der the conditions existing in Gymnomenia. Here, on the one hand, the 
longitudinal musculature is very feebly developed, and, on the other, 
the latero-ventral fibres of the septal muscles cross each other in a 
manner recalling that of Chiton. Thus the musculature of Chiton 
and Gymnomenia offers good homologies (cf. also THIELE 1902, p. 
310). But the similarity to Chiton is still more perfect, in as much 
as a lateral concavity exists in Gymnomenia at the insertion of the 
strongest cords. In this furrow we probably have the rudiment of 
