134 A. OKA. 



appronrh those of , ordinavy cells in size and appearance. The outer 

 limit of this layer is by no means definite, gradually losing itself in 

 the granular mass. 



As the sac elongates, it becomes constricted at the middle, divi- 

 ding into an outer and an inner chamber. The constriction be- 

 tween the two chambers is the future mouth, and the inner chamber 

 represents the future oesophagus and the stomach. The outer cham- 

 ber soon ac<|uires the form of a hollow cone, at the base of which the 

 mouth opens and which tapers towards the outer opening. At the 

 base of this conical chamber the epithelium is especially thickened and 

 eventually gives rise to the lophophore and the tentacles, the chamber 

 itself being the tentacular sheath. The investing layer derived from 

 the o'ranular cells (lin. epitli.') become more and more conspicuous, 

 and lines the entire outer surface of both chambers. 



The lophophore is at first a semicircular ridge, clasjông the 

 mouth on that side which corresponds to the original bottom of ihe 

 cystogenous c ip (convex side). The ridge arises by the folding of 

 the wall, in which process both layers arc concerned. The ends oi" 

 this semicircular ridge are prolonged in the form of free finger-like 

 processes, the rudiments (^f lophophoral arms. The interior of the 

 h>phophoral rudiment is occupied by the granular mass as soon as it 

 is formed. The developing polypide lies on its anal side when the 

 statoblast is placed on its concave side. 



Another constriction divides the lower chamber into the oeso- 

 phagus and stomach. The stomach begins to send a hollow process 

 upward to form the intestine (fig. 51, PL XX. Intest.). 



The free edge of the lophophoral rudiment is divided into a series 

 of knobs, which are conspicuous nearer the median line, becoming 

 gradually smaller towards the tips of the arms. These knobs are the 

 origin of the outer row of tentacles. In the meanwhile, a second 



