GAMETOGENKSIS AND FERTILISATION IN NEMATUS RIBESIT. 101 



Gametogenesis and Fertilisation in Nematus 



ribesii. 



By 

 L.. Doiicnstei', ITI.A., 



Late Mackinnon Student of the Royal Society; Lecturer in Zoology in 

 the University of Birmingham. 



With Plate 8. 



In a previous paper ^ I gave an account of the maturation 

 and behaviour of the polar nuclei in several species of 

 sawflies which develop parthenogenetically. 



In all these species there were two maturation divisions, 

 giving rise to an egg nucleus and three polar nuclei, and in 

 some cases fusion took place between the second polar 

 nucleus and the inner half of the first. The egg nucleus 

 sank into the yolk and began to divide to form the embryo, 

 while the polar nuclei in all cases ultimately disintegrated. 

 Since whenever the chromosomes were clearly visible their 

 number appeared to be eight, both in the maturation mitoses 

 and in the later divisions in body-cells, it was concluded that 

 no reduction in the ordinary sense took place. But if 

 fertilisation ever takes place by conjugation of male and 

 female pronuclei, an obvious difficulty arises with regard to 

 the chromosome number in fertilised eg-gs, and since the 

 process of fertilisation had not been thoroughly examined at 

 the time when the paper referred to was written, it was 

 necessary to leave the question open in the hope of finding a 

 satisfactory answer later. This paper gives an account of 

 1 'Quart Journ. Micr. Sci.,' vol. id, 1906, p. 561. 



