FERTILIZATION ON PARTHENOGENESIS. 175 



In the experiments here presented we have clearly depicted a 

 set of conditions, each somewhat different from the others, 

 that reveal gradations from the normal condition to the boundary 

 line of the possibilities, and even to a complete absence of the 

 fertilization reaction. We have no indication that the processes 

 of activation resulting in complete membrane production are 

 different, in any of the different methods by which it may be 

 called out. But two things we see in common (i) the non- 

 fertilizible condition of the egg whether produced by the addi- 

 tion of sperm or as a result of artificial stimulation and (2) the 

 absence of fertilizin. While eggs are in this non-fertilizable 

 condition sperm may enter them in great numbers, but are not 

 more efficient in producing further developmental phenomena 

 than in the case of unripe eggs. 



We see further that exposures to the same substances used to 

 call out membranes can be conducted so that no membranes are 

 produced (indication of quantitative phase of activation) and 

 that the addition of sperm does permit a certain amount of 

 development; but this development is usually very widely separ- 

 ated from the normal. In all instances where treatment with 

 these agents permits any effect of the spermatozoon at all, 

 fertilizin has been present in quantities sufficiently large to be 

 detected by its property of agglutinating sperm. 



Also by exposing ripe eggs to butyric acid, both for the opti- 

 mum time to produce membranes, and for a prolonged exposure, 

 conditions have been produced in which the eggs appear normal 

 but yet addition of sperm does not result in development. We 

 have determined that sperm penetrates these eggs but are never- 

 theless ineffective ; fertilization is entirely lacking. Also in these 

 instances we have always encountered an absence of fertilizin. 

 Thus it is fairly well established that wherever fertilization is 

 possible fertilizin is present. With this so thoroughly indicated 

 the answer to our question Can fertilization be superposed 

 upon parthenogenesis is very easily answered. 1 When an 



1 It appears that some artificial agents have the power of calling forth a certain 

 amount of development without inducing cortical changes of the egg. Hypertonic 

 sea water, as shown by Loeb, in certain instances may cause development but it 

 is not always capable of doing so. Just what conditions are necessary for its 

 action are still not well understood and I shall defer any discussion of its effects 

 until a later date. 



