l86 UNIVERSITY OF MISSOURI BULLETIN 



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If we mean by development the whole cycle from the 

 egg to the old age and death of the adult, we may mention 

 at this point some other tantalizing problems which must be 

 solved, if at all, by the experimental method. The certainty 

 of death holds for the individual body of the many-celled form 

 throughout the animal world, but not for all parts of the 

 body, since from some of the germ cells comes the next 

 generation. Hence, the germ cells perish only when the race 

 ceases to exist. We sometimes state this by saying that, while 

 the body perishes, the germ cells are "immortal." Why is it 

 that one cell or group of cells is able under certain conditions, 

 namely, union in fertilization with another germ cell, to con- 

 tinue its life in the body of the next generation and so con- 

 ceivably to all future generations, while its neighbor, a cell 

 of the same body, is destined only for old age and death? 

 Why is there this difference between germ and body or somatic 

 cells? Save for cases of normal parthenogenesis, the germ 

 cells always die unless they unite in fertilization. Their con- 

 tinued existence hinges upon this one condition. If so slight 

 a thing determines life or death for the germ cell, why is 

 it that we cannot do something for the body or soma? It 

 may not be all a dream to hope that we may some day 

 analyze the conditions of this somatic death and germinal 

 immortality to such an extent that death as a natural process 

 may become at least longer delayed. 



The whole question of development is a never ending 

 wonder to the closest student as well as to the novice, and s© 

 manifold has been the work of recording merely the sequence 

 of the stages in the life cycles of different forms, that it is 

 small wonder we are only now entering upon an analysis 

 of the process by a rigorous application of the experimental 

 method. In this work, experiment and observation must go 

 on side by side, must indeed be inextricably interwoven ; but, 

 whereas in the past we have been the more concerned with 

 a description of the sequence of stages, in the future we 



