PROCESS OF REPRODUCTION IN ORGANISMS. 3 



believe that the facts do not warrant such a designation. The 

 cells are in many cases functional parts of the organism and even 

 their histological characteristics indicate that they are by no 

 means indifferent or reserve cells. Cases in point are the 

 parenchyma of the flat worms and the peritoneal epithelium of 

 polychaetes. Apparently in many cases such cells have been 

 called indifferent not because of their embryonic appearance, but 

 because they are capable of forming other parts or of giving 

 rise to germ cells. If we are to hold to the morphological criterion 

 of differentiation then these cells certainly undergo dedifferentia- 

 tion before they redifferentiate. 



The assumption of the existence of accessory germ plasm to 

 account for such cases is entirely unnecessary and superfluous. 

 If protoplasm is a physico-chemical substance why is it necessary 

 to assume the continuous existence ot a given specific constitution. 

 Other substances in nature are capable of changing their con- 

 stitutions in one direction or another under certain conditions, 

 while under others they may return to their original constitution. 

 Some of the most fundamental laws of physics and chemistry 

 are based upon this fact. Moreover, we know that in the meta- 

 bolic processes of organisms substances may be built up under 

 certain conditions and decomposed under others. What con- 

 ceivable reason have we for assuming before we have tested all 

 possibilities that these same laws do not hold good for whac we 

 are accustomed to call germ plasm? 



In short, the evidence of our senses teaches us that in the 

 isolated pieces capable of regulation something identical with 

 or approaching more or less closely to the so-called germ plasm 

 of the species appears de novo in consequence of the isolation and 

 that this substance reacts in a definite specific manner essentially 

 similar to the reaction of other isolated masses of the protoplasm 

 of the species. Here then is a case of reproduction for which 

 the assumption of continuity of the germ plasm is purely gratui- 

 tous. Whenever in such organisms the conditions which induce 

 differentiation disappear the differentiation disappears to a 

 greater or less degree, in part through the destruction of the more 

 highly differentiated cells and in part through the dedifferentia- 

 tion of the less highly differentiated cells which are then capable 



