ONTOGENY OF THE ANNULUS VENTRALIS. 



133 



successive parts of a zig-zag suture. The inner course of the 

 groove is more sinuous than before in correspondence with the 

 increased bending of the invagi- 

 nated shell that forms its walls. / 



/ 



The chief features of the adult ', 



\ 



sperm pocket are thus present \ 

 except that the anterior orifice 

 seems more closed in some indi- 

 viduals. 



Though in some cases itseemcd 

 as if the groove itself did not 

 bend to one side to end under the 

 hood, but rather that the trans- -___ 

 verse fold left a passage from " 

 the groove to the hood, the true 

 state of the epidermal groove upon and in which the shell groove 

 is formed was seen when the shell was pulled off. Then, in Fig. 

 22, enlarged 200 diameters, there is a deep, bent furrow with high 

 sides formed of long epidermal cells, as somewhat diagrammati- 

 cally represented in this camera lucida sketch of an optical section 



FIG. 20. 



FIG. 21. 



FIG. 22. 



of the epidermal part of the receptacle. In this specimen the shell 

 was easily removed since a new shell was in process of formation to 



