1 6 Hewitt, Cytological Aspect of Parthenogenesis in Insects. 



of egCTs not containing a nucleus and obtained embryos 

 from the same disproves the idea that fertilisation is an 

 affair of the nuclei only. 



Nature of Parthenogenesis. 



Parthenogenesis may be regarded as internal agamo- 

 genesis. But it is not by any means of the same nature 

 throughout the group. The polar bodies are now generally 

 regarded, I think, as abortive ova. The experiment of 

 Francotte (36) who was able to fertilise a rather large polar 

 body was satisfactory proof of the fact. It follows then^ 

 that if we regard the polar nuclei as nuclei of abortive 

 ova, or better abortive gametes, there are different kinds 

 of individuals produced in the different types of parthe- 

 nogenesis which we find occurring. 



In Aphis the formation of a second polar body is 

 suppressed, the resulting individual is then developed from 

 a cell the nucleus of which may be taken to represent the 

 fusion of two sister gametes. In Bouibyx mori and 

 Liparis dispar where two polar bodies are formed the 

 individual is a monont,* having developed from a single 

 gamete. In only one case has the complete development 

 of a parthenogenetic ovum, which does not extrude polar 

 bodies, been followed, namely, that of the bee. In this 

 form the second polar nucleus fuses with the inner half 

 of the first polar nucleus, and from the syntelosome 

 so formed, the male germ cells develop. These germ cells 

 develop then, from a nucleus which is really a diont, the 

 result of the fusion of two (abortive) germ nuclei of the 

 relation of cousins. The somatic cells of the bee are 

 derived from the q.^% nucleus. Consequently the drone 

 bee is a compound structure, as Blackman has also pointed 

 out. The germ cells have a different origin from the 

 * I am indebted to Dr. Sharp for this word. 



