260 Chas. W. and G. T. Hargitt. 



Fig. 34. Invagination completed, the entoderm completed and the blastopore 

 closing in the ectoderm layer, 'a' a cell in the coelenteron, 'b' a cell in the cleavage 

 cavity which is apparently migrating into the coelenteron. Drawing made from 

 2 sections. 



Fig. 35. Cross section of a very early planula, showing coelenteron and cleav- 

 age cavity. 



Fig. 36. Longitudinal section of a developing planula. The ectoderm cells 

 have nearly their definite shape and size and in their rapid growth have pulled 

 away from the more slowly growing entoderm. 



Fig. 37. Completed planula, anterior end uppermost. The differences between 

 the ectoderm and entoderm are well shown. The yolk is used up except for a few 

 granules at anterior end. The black bodies are nematocysts. At posterior end 

 the entoderm is differentiating to form a point of attachment for the planula. 



