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PHYSIOLOGY 



be cut off from the parent. The sexual process does 

 not differ in essence from the conjugation of the one- 

 celled animal, but it is necessarily modified by the 

 fact that in a many-celled animal as the cells are 



Fie. 81. — Portion of a colony, gp, reproductive polyp; mp, defensive polyp 

 tp, nutritive polyp. (From McMurrich, after Hincks.) 



differentiated not all of them can enter into the process. 

 Special cells are therefore manufactured by special 

 organs and set apart for reproduction. In one animal 

 they are large, round, quiescent; and in another they 

 are small, irregular, motile. These cells are set free 

 in the water. They meet as the one-celled animals do 



