ONTOGENY 17 



zygote and its daughter cells are not considered in themselves 

 reproductive processes, but as steps (cell divisions) in the 

 building up of the whole new individual, as but one phase in 

 the general process of reproduction. 



Some physiological reorganization of substance, such as 

 ordinarily results from the intermingling of the plasmas of two 

 individuals or lines, seems a necessity for the continued exist- 

 ence and reproductive activity of most organisms. In some 

 Insects (Aphids, etc.), Rotifers, Crustacea, and other forms, 

 reproduction occurs normally, through long periods, without 

 any such syngamic fusion, the new organisms developing from 

 single unfertilized ova (parthenogenesis). While this condition 

 is, in these cases, clearly derived from the normal, yet it seems 

 to illustrate the non-essential relation of syngamy and repro- 

 duction. In such forms syngamy does occur under certain 

 conditions or during certain periods in the life cycle of the 

 organism. For example, the difficult conditions of winter or 

 drought may be successfully withstood by the organism while 

 in the form of the zygote. 



So too in many, perhaps most, Protozoa, reproduction or 

 fission proceeds normally and for long periods without fertili- 

 zation or conjugation. The process of conjugation is opposed 

 to reproduction and may actually inhibit it for a time. Here 

 it appears frequently to be associated with the onset of con- 

 ditions unfavorable to the existence of the organism in its 

 vegetative condition. 



It seems, therefore, that the processes of fertilization and 

 reproduction may not be essentially related, and that the 

 intermingling of the plasmas of two individuals is related 

 directly to phenomena other than reproduction. Such a 

 modification of substance as results from fertilization, however, 

 may be essential to continued existence, and it is certainly true 

 of most Metazoa that such a plasmic fusion is an organic 

 necessity. In the simple Protozoa this may be accomplished 

 at any time by the fusion of two individuals in the form of 

 gametes. In the Metazoa, however, it is obvious that this 

 necessary intermingling of substance occurs only when the 



