29 



anterior edge of the posterior division of the great venous 

 sinus (PI. VII, fig. 53, £3^3), to the wall of which it is 

 attached by connective tissue. Ventrolateral^ (he 

 envelope is reinforced by the depressor muscles of the 

 funnel. Dorsolaterally ii is similarly strengthened by 

 the great lateral cephalopedal muscles. 



General conclusions. — Considering Eledone as a type 

 of the Cephalopod organisation, the following characters 

 are noticed : — 



1. It retains the primitive bilateral symmetry of the 

 Phylum, and hence in this respect is less specialised than 

 many Gastropods such as Helix. 



2. On comparison with more primitive members of 

 the Phylum, e.g. Chiton, it is seen thai profound changes 

 have evidently occurred in the inter-relations of the head, 

 foot and visceral dome. The alimentary canal has turned 

 forward posteriorly, so becoming U-shaped. The anus 

 has been ventrally approximated to the mouth, the free 

 ends of the gills point anteriorly, the true morphologically 

 ventral surface of the body has been greatly abbreviated, 

 and the dorsal correspondingly lengthened. The mantle 

 now lias the form of a pouch or sac, enclosing the visceral 

 dome. Simultaneously with these changes the foot ceased 

 to be used merely as a ventral creeping organ, and was 

 transformed into a circumoral mass. Probably this was 

 effected by the lateral regions of the foot growing up 

 dorsally, on each side of the head, and finally fusing above 

 it, the anterior ede;e meanwhile browing 1 out into long 

 flexible processes. 



