THE BIOLOGY OF THE CELL SURFACE 



Experimental parthenogenesis, a problem far from being 

 solved, invites investigations both for its own sake and for 

 the implications it possesses for the biology of cells gener- 

 ally. In the interest of this research it is necessary to 

 define the problem clearly in order that not all kinds of 

 observations are considered as belonging to it: Experimental 

 parthenogenesis must be defined as the development of an 

 egg that has been initiated and carried to at least the 

 normal larval stage by an agent other than the living 

 spermatozoon. 



In contrast to this clear definition there exists a great 

 deal of confusion in the literature on this subject. For 

 instance, an agent which produces almost no change in an 

 unfertilized egg, as revealed by the egg's response with 

 perfect development when inseminated, is often called a 

 parthenogenetic agent. Or the so-called parthenogenetic 

 agent induces membrane-separation only, stimulating the 

 egg to the limited extent that makes fertilization now impos- 

 sible. In other cases the changes induced may be injurious, 

 yet the egg does not lose capacity to respond to fertiliza- 

 tion, though its development is abnormal. Or the pseudo- 

 parthenogenetic agent induces cytolysis which begins sooner 

 or later, depending upon the agent's toxicity. Whenever 

 the changes induced, either because of the nature of the 

 agents themselves or the method with which they are used, 

 do not lead to development, they should not be called 

 parthenogenetic. And certainly, death changes, i.e., cyto- 

 lysis, should be considered to be beyond the limits of the 

 term, the initiation of development. 



The establishment of the mitotic figure constitutes, as 

 we have seen, a definite and reliable index for the comple- 

 tion of the fertilization-process. Normally, development 

 then proceeds with rhythmical nuclear break-down and 

 reformation; and in the majority of eggs this division of 

 the nucleus synchronizes with cleavage of the cytoplasm. 



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