188 GENERAL BIOLOGY 



formation into a typical protozoan may take place. 

 Such a transformation of the old tissue, unaccom- 

 panied by growth, is called regulation. A striking 

 example is found in the reaction of young embryonic 

 stages. If, for example, the blastula of a sea- 



FIG. 69. Regeneration of the blastula and gastrulse of sea-urchins ; 

 the line indicates where the blastula or gastrula was cut in half; the 

 smaller figures show results of the regeneration (regulation) of the two 

 halves of each. (From Jordan and Kellogg.) 



urchin be cut in two, each half-sphere will close over, 

 round up, and form a perfect blastula, half the original 

 size. Each of these goes through its normal trans- 

 formations, and the end-result is two individuals 

 instead of the single one that began its course of 

 development. 



