REPRODUCTION. 



105 



tion with one another, with the result that a compound 

 organism is produced, consisting of a collection of nutritive 

 factors or "polypites," organically united, but enjoying a 

 semi-independent existence. In this phase of its life we 



Fig. 29. Group of zpoids of Hydractinia echinata. Enlarged (after Hincks). a a 

 Nutritive zooids ; b b Generative zooids, carrying sacs filled with ova. 



may compare Hydractinia with a tree composed of numer- 

 >bus leaf-buds borne upon a branched stem, but not yet 

 exhibiting flowers. Such a comparison would involve some- 

 thing more than a mere superficial resemblance. The 

 ordinary zooids of Hydractinia are produced by a process 



