DEVELOPMENT OF HYDRA 



239 



Fig. 50. 



/elopment of Hydra. A, the ovum filled with deutoplasts ; ec, 

 ectoderm of the parent Hydra ; mg, mesogloea ; en, endoderm ; 

 B, blastula stage, in which some cells of the blastula wall are 

 passing in towards the interior ; blc, segmentation cavity or 

 blastocoele. C, the blastocoele nearly filled up by immigrant cells. 

 D, an embryo further developed with sh, an external spiny, and shi, 

 an internal protective case ; ec, ectoderm ; z", inner solid mass of 

 cells. E, the embryo still enclosed in its double protective case, 

 flattening itself out. F, the embryo creeping out of its protective 

 cases ; lettering as in A and D. G, the empty case after escape of 

 the embryo. (D, original ; the rest after Brauer.) 



