COMPARATIVE ANATOMY 







Fig. 56. 



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

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

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

 passing in towards the interior ; blc, segmentation cavity or 

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

 D, an embryo further developed with sk, an external spiny, and sJii, 

 an internal protective envelope ; ec, ectoderm; 7", 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 

 envelopes ', lettering as in A and D. G, the empty envelope after 

 escape of the embryo. (Z>, original ; the rest after Brauer.) 



