DEVELOPMENT OF HYDRA 



239 





Fig. 50. 



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

 ectoderm of the parent Hydra; m£, mesoglosa ; en, endoderm ; 

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

 passing in towards the interior ; die, segmentation cavity or 

 blastocosle. C, the blastoccele nearly filled up by immigrant cells. 

 Z>, an embryo further developed with sk, an external spiny, and skz, 

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

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

 flattening itself out. J^, the embryo creeping out of its protective 

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

 the embryo. {B, original ; the rest after Brauer.) 



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