494 REIGHARD—PHELPS. [ Vou: axis 
to support the increased weight. Assuming that such an in- 
crease in size has come about in Elasmobranchs through yolk 
accumulation, the adhesive organ of these forms has conse- 
quently become useless and has been reduced. It persists in 
but three genera in the form of the anterior head cavities. 
Since an adhesive organ of this form is useless to a larva 
greatly burdened with food yolk, its retention in Ganoids indi- 
cates that the ova of these fishes have not at any time pos- 
sessed more food yolk than they now have. The Ganoid ovum 
is not to be derived from that of the Elasmobranch through 
secondary reduction in the amount of food yolk. Beard’s 
(1890) contention on this point is thus upheld. Hence we 
must conclude that the Ganoid and Elasmobranch lines sep- 
arated before the great accumulation of yolk in the ova of 
Elasmobranchs had taken place. 
Amphioxus. Here there is found a pair of diverticula at 
the anterior end of the foregut. Of these anterior gut 
pouches the right becomes the head cavity of Amphioxus, 
while the left acquires an opening to the exterior and is finally 
converted into the Raderorgan, a lobed tract of ciliated epi- 
thelium which surrounds the mouth. The left anterior gut 
pouch of Amphioxus thus agrees with the adhesive organ of 
Amia in opening to the exterior. Neal (1898) has already 
homologized these anterior gut pouches of Amphioxus with 
the anterior head cavities of Elasmobranchs. If this be con- 
ceded, they are in turn homologous to the adhesive organ of 
Amia. The evidence at hand does not seem to us to warrant 
any other conclusion, though possibly it does not warrant any 
conclusion. 
SUMMARY OF CONCLUSIONS. 
The adhesive organ of Amia (and Lepidosteus) is in no 
way homologous with epidermal sense organs as claimed by 
Balfour (1881) and Dean (1896). It is a pair of gut pouches 
comparable to the anterior head cavities of Elasmobranchs. 
These anterior head cavities may therefore be interpreted as 
adhesive organs which have been rendered useless by the in- 
