ONTOGENESIS 



187 



undifferentiated mass of living matter, derived from 

 an organism which also conforms to that specific type. 



Regulation. Redifferentiation, in the case of 

 injury or alteration of form, is not always accom- 

 panied by growth of new tissue. If a Hydra be 

 cut in two, each half will transform into a complete 



FIG. 68. 'Regeneration of Stentor : A, cut in three pieces; B, row 

 showing regeneration of the anterior piece ; C, regeneration of middle 

 piece; D, that of posterior piece. (From Jordan and Kellogg, after 

 Morgan.) 



Hydra, half the original size. Here there has been 

 no new growth, but a readjustment and shifting 

 of mutual relations of the old tissues of the animal. 

 Among the larger Protozoa, such as Stentor, the same 

 thing occurs if the cell be cut in fragments. It is 

 necessary, however, for each fragment to contain a 

 portion of the original nucleus in order that the trans- 



