474 REIGHARD—PHELPS. [Vor. XIX. 
form the fundaments of the adhesive organ. ‘The central and 
smallest of them lies in the middle line between the other 
two and directly in front of the forebrain. It will be spoken 
of as the button. Bounded outside by a curved white line, 
and inside by the branchial area, are seen the halves of the 
body cavity extending backward over the yolk about the 
sides of the head. Between the three protuberances and the 
white line the stomodaeum appears as a long crescent-shaped 
depression. 
pe. dix. 
Fic. B.—Portion of a parasagittal section of an embryo of the stage 
shown in Plate, Fig. 2. The section passes to one side of the 
median plane through the optic vesicle and one-half of the adhesive 
organ. Camera outline; details from photograph. X about 150. f. g., 
foregut; h., heart; i. ect., inner layer of ectoblast; 0. ect; outer layer 
of ectoblast; op. v., optic vesicle; pc. c., pericardial cavity; pd. div., 
one of the paired diverticula of the foregut (fundament of the ad- 
hesive organ); st., stomodaeum; ylk., yolk. 
Sections of embryos of this stage (Fig. B) show that the 
entoderm in front of the crescent has been folded backward 
so as to form a small part of the ventral and side walls of 
the foregut at its anterior end. Ventral and anterior to the 
lower foregut wall thus formed and filling the entoderm fold, 
is the large pericardial cavity within which is seen the heart. 
Ventral to the pericardial cavity lies a portion of the yolk 
