424' BIOLOGY: GENERAL AND MEDICAL 



the amputated head of a snapping turtle to bite and 

 hold fast to a stick, or in the tendency of a decapitated 

 rattlesnake to coil and strike, we see examples of pro- 

 longed molecular or cellular animation after somatic 

 death has occurred. 



If we descend still lower, it becomes impossible to 

 make any clear differentiation between the somatic 

 and molecular death except by experiment. Thus, 

 when an earth-worm is chopped to pieces, all the frag- 

 ments live on for a considerable time many days and 

 it is only experience with the regenerative powers of this 

 animal that enables one to predict which fragments 

 may, and which may not live and form new worms. 



Still more interesting is the condition found in the 

 hydra. The animal is cut to pieces, each piece draws 

 itself together, becomes inactive and apparently dead, 

 but after a time quite small pieces may rearrange the 

 substance, fit themselves for further growth and may 

 recover. 



The relation of molecular to somatic life and death 

 depends upon the degree of specialization attained by 

 the cells and their ability to maintain more or less 

 independence under unfavorable condition. 



This is well exemplified by the behavior of plants 

 among whom somatic life is very slightly differentiated 

 from molecular life because of the absence of such special- 

 ized organs as those controlling the functions of circula- 

 tion, innervation, respiration, and digestion in animals. 

 Partly for this reason and partly because of the general 

 diffusion of reproductive energy among the vegetative 

 cells, portions of many plants cut off from the parent and 

 placed under appropriate conditions live on, grow well, 

 and soon renew the whole plant. 



The somatic life of each individual eventually comes 

 to an end, but the life of the germ-plasm persists in its 

 descendants in a succession of ever-changing forms for 

 which one can see no end so long as the physical condi- 

 tion of our planet continues to afford such conditions of 



