a 
‘BLEDONE. 497 
antericr edge of the posterior division of the great venous 
ous Pile Vil, te. 53, S,V,), to the wall of which 11 is 
attached by connective tissue. Ventrolaterally the 
envelope is reinforced by the depressor muscles of the 
funnel. Dorsolaterally it is similarly strengthened by 
the great lateral cephalopedal muscles. 
General conclusions.—Considering Hledone 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 that 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 has 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 edge meanwhile growing out into long’ 
ftexible processes. i 
