OAMETOGENESIS AND FERTILISATION IN NEMATDS RIBESH. 109 



(synapsis) of chromosomes takes place before the maturation 

 divisions, resulting in the separation of complete chromosomes 

 at one of the mitoses, while in other eggs no pairing takes 

 place, and each chromosome undergoes two equational divi- 

 sions. In connection with this it is noticeable that in the 

 eggs having the equational type the eight chromosomes are 

 about half the size of the four seen in reduced eggs. 



I have found the reduced type in eggs from both virgin 

 and impregnated females, so that the view which first sug- 

 gested itself, viz. that reduction only takes place in eggs 

 which contain spermatozoa, is not tenable. 



Re-examination of my sections of Poecilosoma lutecium 

 confirms me in the belief that in that species, which yields 

 females from virgin eggs, and is normally not fertilised, there 

 are two equational divisions in all the eggs of which I have 

 suitable preparations. ^ /{u.^j^^j} 



In the developing egg the somatic mitoses of fertilised 

 eggs appear always to have eight chromosomes; a larger 

 number has never been found. This is what would be 

 expected if only eggs which undergo reduction are capable 

 of fertilisation. 



In virgin eggs commonly eight are found, but in some cases 

 the equatorial plate seems to have four only, showing that 

 reduced eggs when not fertilised can develop as far as the 

 blastoderm stage (fig. 22). The number of eggs which die 

 before hatching varies, in some batches being very small, in 

 others more considerable; it is possible that the reduced eggs 

 are those which fail to develop to larvee. Since, however, it 

 has been shown by the mitoses in the ovary sheath that the 

 chromosomes are possibly compound, it may happen that 

 reduced eggs which are not fertilised restore the normal 

 number of chromosomes by division of the compound chro- 

 mosomes, as was asserted by Petrunkewitsch (loc. cit.) with 

 regard to the bee. 



The conclusion that the eggs of one species may either 

 undergo reduction, or may retain the full number of chromo- 



