200 The Mechanistic Conception of Life 



fertilization. The reader knows that the eggs of the over- 

 whelming majority of animals cannot develop unless a sperma- 

 tozoon enters them. In this case a living agency is the cause of 

 development and the problem arises whether it is possible to 

 accomplish the same result through the application of well- 

 known physico-chemical agencies. This is, indeed, true, and 

 during the last ten years livuig larvae have been produced by 

 chemical agencies from the unfertilized eggs of sea-urchins, 

 star-fish, holothurians, and a number of annelids and moUusks; 

 in fact this holds true in regard to the eggs of practically all 

 forms of animals with which such experiments have been tried 

 long enough. In each form the method of procedure is some- 

 what different and a long series of experiments is often required 

 before the successful method is found. 



The facts of artificial parthenogenesis, as the chemical 

 fertilization or activation of the egg is called, have, perhaps, 

 some bearing on the problem of evolution. If we wish to form 

 a mental image of the process of evolution we have to reckon 

 with the possibility that parthenogenetic propagation may have 

 preceded sexual reproduction. This suggests also the possi- 

 bihty that at that period outside forces may have supplied the 

 conditions for the development of the egg which at present the 

 spermatozoon has to supply. For this, if for no other reason, a 

 brief consideration of the means of artificial parthenogenesis 

 may be of interest to the student of evolution. 



It seemed necessary in these experiments to imitate as 

 completely as possible by chemical agencies the effects of the 

 spermatozoon upon the egg. When a spermatozoon enters the 

 egg of a sea-urchin or certain star-fish or annelids, the immediate 

 effect is a characteristic change of the surface of the egg, namely, 

 the formation of the so-called membrane of fertilization (Figs. 

 1 and 2). The writer found that we can produce this mem- 

 brane in the unfertilized egg by certain acids, especially the 

 monobasic acids of the fatty series, e.g., formic, acetic, propionic. 



