GAMETOGENESIS AND FERTILISATION IN NEMATUS RIBESII. 107 



all the mitoses observed the number is more than eight ; 

 usually it seems to be sixteen, but in some cases the figure 

 suggests more than sixteen very small chromosomes (fig. 

 16a — f). Wilson' has described spindles with double the 

 somatic number in the ovarj^-sheath of Hemiptera, and 

 regards them as abnormal, but the figures seen in N. ribesii 

 certainly suggest that the eight chromosomes in the primi- 

 tive germ-cells are compound, composed of a greater number 

 of smaller units, possibly more than sixteen. 



In the pupal ovary the egg-cells are already definitely 

 formed, and do not divide further, but merely undergo the 

 usual growth with deposition of yolk. The follicle cells are 

 now quite small, and an occasional mitotic figure is visible ; 

 these are rarely clearly defined, but appear to have eight 

 chromosomes. When the egg has reached its full size the 

 follicle cells become degenerate, with obscure dark-staining 

 nuclei. Groups of similar degenerating cells are found here 

 and there in the larval ovary. 



The fact that the chromosome number in the ovary, and 

 probably in the follicle cells, is smaller than that found in the 

 sheath is of considerable interest. 



In addition to the case described by Wilson, and referred 

 to above, the same kind of thing has been observed by 

 Petrunkewitsch in the bee," in which he found the unreduced 

 number to be sixteen in the egg, but sixty-four in the blasto- 

 derm, and it is still more conspicuous in Ascaris, which, 

 according to Boveri, has a large number of very small chromo- 

 somes in the somatic cells, but only four in all the cells on the 

 *' germ-track," from the fertilised egg up to the maturation 

 divisions of the germ cells.^ These facts suggest that it may 

 happen not infrequently that the chromosomes in cells of the 

 germ-track may be compound, and consist of a number of 

 smaller units which become separated in somatic cells. But 



1 " Studies oa Chromosomes," ill, Mourn. Exp. Zoo.,' vol. iii, No 1, 190G. 



2 ' Zool. Jahrb.,' vol. xiv, 1901, Anat. uud Ontog., p. 573. 



' Boveri, 'Ergebnisse iiber die Konstitution der Cliromatischen Substanz 

 des Zellkerns.' (Fischer, Jena.) 



