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HYDRA 



sorbing nutriment from them, thus continually increasing 

 in size at their expense. Ultimately the ovary comes to 

 consist only of this single amoeboid ovum, and of a layer of 

 superficial cells forming a capsule for it. As the ovum grows 

 v oik-spheres (Fig. 53), small rounded masses of proteid 

 material are formed in it, and in Hydra viridis it also acquires 

 green chromatophores. 



When the ovary is ripe the ovum draws in its pseudopods 

 and takes on a spherical form : the investing layer then 







FIG. 53. A, Ovum of Hydra viridis, showing pseudopods, nucleus 

 (gv], and numerous chromatophores and yolk spheres. 



B, a single yolk sphere. (From Balfour after Kleinenberg.) 



bursts so as to lay bare the ovum and allow of the free access 

 to it of the sperms. One of the latter conjugates with the 

 ovum, producing an oosperm or unicellular embryo. 



The oosperm divides into a number of cells, the outer- 

 most of which become changed into a hard shell or capsule. 

 The embryo, thus protected, falls to the bottom of the water, 



