236 



ANIMAL BIOLOGY 



up a new vista of the regulatory powers of living things from 

 Protozoon to Vertebrate and from egg to adult, and has afforded a 

 means of approach to some fundamental biological problems. And 

 withal it has a practical value. The surgeon now knows more about 

 the regeneration of tissues in general and of nerves in particular in 

 wound healing, and the oysterman knows — or should know — 

 that his attempt to destroy Starfish by tearing them up and throw- 

 ing the pieces overboard may serve merely to increase this enemy 

 of the Oyster. (Figs. 46, 159-161.) 



/mm 



Fig. 159. — Regeneration in a Flat worm, Lineus socialis. A, normal worm; 

 B, B', section cut from body and its appearance after twelve days; C, same 

 after thirty days, cut in planes 3-3 and 4-4. Successive cuttings and regenera- 

 tions indicated by arrows. M, M', similar experiments and results on posterior 

 end of body. (From Coe.) 



The power of fragments of distinctively somatic tissue, as in 

 many lower animals and plants, to form a complete organism 

 including the reproductive organs and germ cells, indicates that 

 we must postulate at least a potential supply 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 discussed. 



