Modification of Germinal Constitution of Organisms 253 



after a time replace the parent species to a considerable 

 extent, if not completely. 



C. Discussion — Summary 



Probably no question in biology has received more 

 attention, and certainly few are so little understood, as the 

 method whereby those variations which are productive of 

 permanent change arise and become incorporated into the 

 germinal constitution of the race. If the possibility of 

 variations arising in a manner like that assumed in the 

 neo-Lamarckian conception be admitted, it must also be 

 admitted that there is at present no critical evidence of any 

 such method of origin. As far as experience warrants a 

 conclusion, there is at present no escape from the general 

 proposition that all variations that are productive of per- 

 manent germinal changes, arise primarily in the germ and 

 appear secondarily in the soma. It must be understood 

 that by this proposition it is not asserted that it is the only 

 possible conception, but that it is the only one concerning 

 which there is at the present time any definite proof. 



Knowledge concerning the germ cells, which are the 

 germ plasm or else the carriers of it, is largely anatomical in 

 character, derived from studies in cytology and in the main 

 is one sided, incomplete, and has been too much directed to 

 the study of the chromosomes. That this is the condition 

 is not strange when one considers the wonderful regularity 

 with which the chromosomes are divided between the 

 daughter cells, and the precision and regularity of the process 

 immediately preceding and accompanying fertilization. 

 These phenomena, so fundamental and common to all 

 organisms, have impressed biologists profoundly and very 

 naturally the opinion arose that the chromosomes were the 



