UYDRA 279 



stituent individuals, or zooids. Thus in the simplest cases 

 among the nettle animals we have crawling zooids, or stolons, 

 and feeding zooids. In other species we have, in addition, 

 reproductive zooids, netthng zooids, and passive, thorn-like 

 zooids. These zooids are, in their earliest stages, ecjuivalent, 

 and seem to have the power of developing into the same thing. 

 Nevertheless some of them develop into very imperfect indi- 

 viduals incapable of exercising anj^ active function. These 

 organized colonies are interesting from a sociological stand- 

 point because they illustrate the complete suljserviency of the 

 individual to the good of the community. This subserviency 

 is found in all successful colonies of animals. 



Regeneration. — Closely alhed to the power of budding is 

 that of reproducing a lost organ. Supposing the " head " 

 (mouth and tentacles) of a Hydra to be cut off, the base will 

 reproduce the lost head. Suppose the base to be removed, 

 the head will reproduce a new base. When a Hydra is cut in 

 two transversely, two Hj^dras result where formerly there was 

 only one. Even three or more Hydras may arise when a 

 Hydra has been cut into so many pieces. Where other condi- 

 tions are favorable to life, you can hardly kill a Hydra by mu- 

 tilation. A trace of this capacity for regeneration, as it is 

 called, is seen also in man when a wound heals and a diseased 

 organ, even when partly destroyed, is made whole again. 



