222 



FOUNDATIONS OF BIOLOGY 



overboard, serves merely to increase many fold this enemy 

 of the oyster. (Figs. 121, 122.) 



The power of fragments of distinctively somatic tissue, as 

 in the Earthworm and many plants, to form a complete 

 organism including the reproductive organs and germ cells, 

 indicates that we must postulate at least a potential supply 



r\ 



FIG. 121. Regeneration and grafting in the Earthworm. A, regeneration of re- 

 moved anterior segments by the posterior piece. B, regeneration of posterior seg- 

 ments by the posterior part, so that the worm has a ' tail ' at either end. C, regenera- 

 tion of removed posterior end by the anterior piece. D, three pieces grafted together to 

 make a long worm; E, two pieces grafted to form a worm with two 'tails'; F, short 

 anterior and posterior pieces grafted together. Regenerated portions are dotted. 

 (From Hegner, after Morgan.) 



of the germ residing in the somatic tissue, which can make 

 good the definitive germ cells when they are lost. At first 

 glance this may seem to be a far cry to save an idea, but it is 

 a fact that there is a continuity of the nuclear complex (GERM 

 PLASM) whether the germ cells are set aside early in individual 

 development, or later by the transformation of what seem to 

 be typical somatic cells. That this is really the crux of the 

 question will be appreciated after the details of cell division 

 have been described. 



