Artificial Parthenogenesis 251 



as in the domain of fertilisation. The reader knows that the eggs of 

 the overM'helming majority of animals cannot develop unless a 

 spermatozoon 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-kno^vn 

 physico-chemical agencies. This is, indeed, true, and during the last 

 ten years living larvae have been produced by chemical agencies 

 from the unfertilised eggs of sea-urchins, starfish, holothurians and 

 a number of annelids and molluscs ; 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 somewhat d liferent and a long series of experiments 

 is often required before the successful method is found. 



The facts of Artificial Parthenogenesis, as the chemical fertilisa- 

 tion of the eg^ 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 possibility 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 partheno- 

 genesis 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 efiects of the spermatozoon upon 

 the egg. "Wiien a spermatozoon enters the egg of a sea-urchin or 

 certain starfish or annelids, the immediate eflfect is a characteristic 

 change of the surface of the egg, namely the formation of the so-called 

 membrane of fertilisation. The writer found that we can produce 

 this membrane in the unfertilised egg by certain acids, especially the 

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

 butyric, etc. Carbon-dioxide is also very efficient in this direction. 

 It was also found that the higher aci(^ are more efficient than 

 the lower ones, and it is possible that the spermatozoon induces 

 membrane-formation by carrying into the egg a higher fatty acid, 

 namely oleic acid or one of its salts or esters. 



The physico-chemical process which underlies the formation of 

 the membrane seems to be the cause of the development of the egg. 

 In all cases in which the unfertilised egg has been treated in such a 

 way as to cause it to form a membrane it begins to develop. For 

 the eggs of certain animals membrane-formation is all that is 

 rcfiuired to induce a complete development of the unfertilised egg, 

 e.g. in the starfish and certain annelids. For the eggs of other 

 animals a second treatment is necessary, presumably to overcome 



