No. 2.] THE ADHESIVE ORGAN OF AMIA. 471 
to be much broader. Opposite this broader part the audit- 
ory pit is found in sections. The broadening itself is due 
in part to the proliferation of cells from the ganglionic ridge. 
The future anterior end of the hindbrain lies just anterior 
to this broader portion. The pointed tip of the forebrain 
extends beyond the optic vesicles which lie close on either 
‘side of it and form the most conspicuous part of the head. On 
each side, behind the optic vesicles and at the side of the brain 
is an elevated, oval area, the branchial area, within which 
~ div. arch. 
ZROres 
Hon LOB Beis 
ch Seat ‘ Ol LL ap — 
S 
srt 
oF 26) S Soro 
Ce OB089 oI Oo RSs 
Oo aS oO rej oYers: 
Fic. A.—Part of a parasagittal section of an embryo along the curved line 
a-b of the stage shown in Fig. 1. Camera outline drawing; details 
from a photograph. div. arch., diverticulum of the archenteron (cres- 
cent) ; ent., entoblast; i. ect., internal layer of ectoblast; o. ect., outer 
layer of ectoblast; op. v., optic vesicle; ylk., yolk. The section passes 
to one side of the median plane and does not include the hypophysis. 
gill slits appear in a later stage. The axial mesoblast shows 
in sections at least twelve trunk somites. In front of the 
optic vesicles and lying against them and the anterior end 
of the brain is a crescent-shaped, elevated area which 1s shown 
by its subsequent history to include the fundament of the 
adhesive organ. It will be referred to hereafter as the cres- 
cent (anterior end of the foregut). 
In a longitudinal section (Fig. A), the archenteron is seen 
to be enlarged slightly at its anterior extremity to form a 
broad, dorsally directed diverticulum which causes the cres- 
