No. 2.] THE ADHESIVE ORGAN OF AMIA. 493 
tions. The central one of these, the “button,” subsequently 
breaks up into mesenchyme, as does the middle portion of the 
pre-oral gut of Elasmobranchs. The lateral portions exist 
as diverticula of the ‘pre-oral gut’ (fundaments of the ad- 
hesive organ). Their relation to the foregut and to the optic 
vesicles and ectoblast is precisely the same as the relation of 
the anterior head cavities of Elasmobranchs to the same struc- 
tures. This is at once evident upon comparing our figure B 
with Neal’s Figs. 7 and 8, Pl. III. These lateral diverticula 
of the foregut of Amia differ from the anterior head cavities 
of Elasmobranchs in their larger size and in the fact that 
their lumina communicate with that of the foregut. These 
differences are referable to the fact that in Amia the diver- ° 
ticula are functional, becoming converted into an adhesive 
organ. In the Elasmobranchs the anterior head cavities are 
not functional as organs, but become converted into mesen- 
chyme. They are potentially diverticula of the foregut. They 
are furthermore in process of reduction, as shown by the fact 
that, while they are still of considerable size in Acanthias 
(Platt, Neal, Hoffmann) and in Galeus (van Wijhe), they 
are much reduced in Scyllium (van Wijhe) and are apparently 
absent in other Elasmobranchs. In these other Elasmobranchs 
the pre-oral gut probably breaks up directly into mesenchyme, 
without first forming the anterior head cavities. 
It seems to us that there can be but little doubt that these 
anterior head cavities were formerly much better developed 
in Elasmobranchs than they now are, and that they were then 
formed as diverticula of the foregut. According to Platt 
(1891) this method of formation still obtains, though this is 
emphatically denied by Neal. We believe these diverticula 
to be homologous with the adhesive organ of Amia. It is 
most probable that the anterior head cavities represent an 
adhesive organ that formerly existed on the end of the snout 
in developing Elasmobranchs. An adhesive organ of the char- 
acter of that of Amia is of use only to larve of relatively small 
size like those of Ganoids and Amphibia. With increase in size 
of the larva the organ becomes useless owing to its inability 
