402 REIGHARD—PHELPS. [Von. XIX. 
origin for the adhesive organ. A further suggestion con- 
cerning a possible homologue in Acipenser of the Amia ad- 
hesive organ will be found in a paper on the development of 
the hypophysis of Amia, by Reighard and Mast (1908). 
Elasmobranchs. lf we regard the adhesive organ of Amia 
as a pair of entoblastic pouches from the anterior end of the 
foregut it becomes an interesting question as to whether there 
exist in other vertebrates similar gut pouches with which they 
may be compared. The head cavities of Elasmobranchs at 
once suggest themselves. We have shown that in Amia the 
first head cavities (pre-mandibular) are formed in the meso- 
blast of the head behind and beneath the optic vesicles. If 
then the adhesive organ of Amia be comparable to a pair of 
head cavities it must be to that pair which lies in front of the 
pre-mandibular cavities, that is to the anterior head cavities of 
Platt. 
The anterior head cavities were first described by van 
Wijhe (1882) in Galeus and later in much more detail by Platt 
(1891, 1891a), Hoffmann (1896) and Neal (1898) in Acan- 
thias. According to the last three observers the foregut ex- 
tends in early embryos nearly or quite to the anterior neuro- 
pore, (Hoffmann, Pl. III, Fig. 19, z, embryos with 15-20 
somites). Hoffmann describes this ‘pre-oral gut’ as becoming 
subsequently divided by the down-growth of the infundibulum 
into a median and two lateral parts. The lateral portions lie 
beneath the optic vesicles and are for a time connected with 
one another by the median portion which extends from the in- 
fundibulum nearly to the neuropore. The median portion of 
the pre-oral gut breaks up finally into mesenchyme. The 
lateral portions develop cavities and become the anterior head 
cavities. After a time the proliferation of cells from the walls 
of these cavities renders them solid. Still later they break 
up into mesenchyme (embryos of 22 mm.) and are no longer 
distinguishable from surrounding mesenchyme. 
The anterior end of the foregut of Amia forms a ‘pre- 
oral gut’ (cf. Fig. C). This becomes divided into three por- 
