398 E. E. JUST. 



differences encountered are doubtless merely incidental. Any ex- 

 planation of experimental parthenogenesis ought, therefore, be 

 congruous it ought to be applicable to all eggs capable of experi- 

 mental initiation of development. 



But there are serious difficulties in the way of reducing all work 

 on experimental parthenogenesis to a common basis. Leaving out 

 work which is manifestly erroneous, we still have a large body of 

 data purporting to deal with " artificial " parthenogenesis which as 

 a matter of fact merely details results in producing membranes, 

 or some slight cortical change, in initiating maturation, etc. In 

 much of this work indubitable death changes are mistaken for 

 cleavage. And we are told that all these are important for science. 

 And even where experimental parthenogenesis is specifically de- 

 nned as the production of cell division many substances are named 

 as agents of experimental parthenogenesis, whereas such agents if 

 allowed to act but an extremely short time either call forth mem- 

 brane separation merely and initiate coagulative death changes. 

 Such results have far less significance for the problem of experi- 

 mental parthenogenesis than death stiffening for the theory of 

 muscle contraction. We are thus forced to discard much of this 

 work also. 



On the other hand, it would be unscientific to reach conclusions 

 for all ova from the results obtained on one. Fortunately, how- 

 ever, we possess many investigations in the field of experimental 

 parthenogenesis of undoubted value. Such, for example, is the 

 work of R. S. Lillie on the egg of Asterias, of Miss Allyn's on 

 the egg of Chcetopterus, in addition, of course, to Loeb's work. 

 Now, in all this work the only common factor is the use of a 

 single agent, heat, butyric acid, or hypertonic sea- water. If we 

 add the eggs of Nereis and of the frog to those just mentioned, 

 we have, with respect to the stage in maturation at which fertiliza- 

 tion takes place or experimental parthenogenesis is possible, all 

 types of eggs represented. It may be generally true, therefore, 

 wherever experimental parthenogenesis is possible, that a single 

 agent suffices. 



In both fertilization and experimental parthenogenesis one fun- 

 damental reaction takes place, namely, the cortical reaction. This 

 is no mere arbitrary assumption. Eggs pass through a period of 



