MaticJiester Memoirs, Vol. I. {igo6), No. ^. 15 



parthenogenesis, as there is no centrosome brought in by 

 a spermatozoon, and in many cases the centrosomes do 

 not appear until the segmentation stages ; we cannot, 

 therefore, look to the centrosome as the cause of Embryo- 

 genesis. 



The suppression of the second polar body in Aphis, 

 and as Brauer (18) found in Artemia, its fusion with 

 the &^^ nucleus, seemed at one time to support Boveri's 

 (13, p. 73) suggestion that parthenogenesis is the result of 

 fertilisation by the second polar body, that is, the second 

 polar nucleus took the place of the sperm nucleus. This 

 suggestion, however, receives no support from the majority 

 •of cases of parthenogenesis in insects, in which there is no 

 fusion of the second polar nucleus with the (t^^ nucleus. 



The complete suppression of definite polar body 

 formation, or at least of the formation of the second polar 

 body may explain the ability of parthenogenetic eggs to 

 ■develop. There may be a cytoplasmic fertilisation, so to 

 speak. The evidence we have, seems to me to suggest 

 that there is a chemico-physical relationship between the 

 nucleoplasm and cytoplasm, which is necessary for the 

 initiation of embryogenesis, and which is brought about 

 by the entrance of the spermatozoon. The non-extrusion 

 of polar bodies may bring about this relationship. What 

 the exact nature of this relationship is, or what are the 

 causes which operate, it is impossible at present to say. 

 It can be brought about by artificial means as Loeb 

 (58-59) Delage (23-27) Petrunkewitsch (77) Morgan (66-69) 

 and others have shown and differences of osmotic pressure, 

 ferments, metallic ions have all been suggested as possible 

 causes, but the problem is still unsolved. 



As Morgan (70) has recently pointed out little atten- 

 tion is paid to the role of the cytoplasm. The work of 

 Delage (29) in Merogony, in which he fertilised portions 



