REPRODUCTION AND LIFE CYCLES 



409 



iiomenoii, involving the creation of new cells by cell division, is a 

 fundamental type of growth. The ability to regenerate lost parts 

 seems to be correlated inversely with the degree of specialization 

 and the extent to which division of labor appears. For example, an 

 unspecialized sponge when pressed through silk bolting-cloth into 

 small fragments will reproduce new individuals. Other more highly 



tyo rzev rays 



two newm^s 



WTone old 

 ray 



two new Tays 



tliree old rays ' ^^^^ 





Vlanavw 



Examples of regeneration in representatives of four different phyla. How may 



such phenomona be explained ? 



specialized forms show less ability to regenerate so completely, but 

 many of the coelenterates as well as certain worms and echinoderms 

 possess this facility of regeneration to a high degree. Starfish, long 

 the enemy of oysters, have increased rapidly in part due to the care- 

 less practice of oystermen who tore them apart and left the frag- 

 ments in the water. It is now known that such disjointed parts, if 

 containing portions of the central disk, are capable of regenerating 

 into new individuals. 



