The Hydra. 



17 



the ovary, which might otherwise become ova. There is thus, 

 it will be observed, a " struggle for existence " among the very 

 cells of a particular organ. Though the egg eats up other cells 

 like an amoeba, the process is not really different from that 



CL 



Kic. 7. — Isolated ectodermic cells of Hydra. Highly magnified. (After Howes.) 



EC, ectoderm cells ; cp, muscular process ; cl, supporting lamella ; ne, nervous 



cells ; T-s, cells entirely detached from supporting lamella ; v, vacuole. 



exhibited by other ova, which, as explained elsewhere, are fed 

 by the cells of the follicle. 



The endoderm is made up of large cells, many of which have 

 one or more vibratile cilia depending from the inner surface ; it 

 is they which bear the chlorophyll corpuscles. Between the 

 two layers is a colourless, thin, structureless membrane, the 



c 



