150 ARTIFICIAL PARTHENOGENESIS [CH, 



the effect produced by shaking Starfish eggs. Larvae ob- 

 tained in this way have been reared through the meta- 

 morphosis to almost or quite adult frogs, which have been 

 found to be both males and females (LoEB, 1918). 



Although, as has been mentioned earlier, the plane of the 

 first segmentation division in fertilised frog's eggs usually 

 depends on the position of the entrance path of the sper- 

 matozoon, it is found that in the parthenogenetic eggs the 

 position of the puncture has no relation to that of the first 

 segmentation plane; this confirms the conclusion that the 

 position of the segmentation plane depends on that of the 

 dividing centrosome introduced by the spermatozoon, and 

 not upon any alteration of the egg-substance induced by 

 the spermatozoon's passage. 



From this short summary of the subject it will be seen 

 that the study of artificial parthenogenesis has led, and is 

 likely to lead still further in the future, to important ad- 

 vances in our knowledge of the physiological or functional 

 aspects of cytology. Not only is it the means of throwing 

 important light on the nature of the metabolic processes 

 concerned in the development of the egg, and of the physical 

 and chemical conditions of cell-division, but it also gives us 

 definite indications of the manner of action of the spermato- 

 zoon in bringing about development. Since eggs which 

 under normal circumstances require fertilisation can develop 

 to larvae or even adults without it, it is clear that the nuclear 

 fusion which is usually regarded as the essential feature of 

 fertilisation is not in itself the cause of development. The 

 spermatozoon, in fact, appears to play two quite distinct 

 parts ; as the bearer of hereditary characters it is equivalent 

 to, and of equal importance with, the egg, but as far as the 

 early stages of development are concerned, it plays quite a 

 minor part, and merely acts as a stimulus to a development 



