492 



ALIST [Vol. XLIV 



In one of the nematode worms of the pheasant he has 

 found that there are two classes of sperm, one with one 

 more chromosomes than the other. Correspondingly, 

 there are two kinds of embryo, male and female, differ- 

 ing by one chromosome in every cell. 



In the classic case of the nematode of the horse, 

 Ascaris niegaloccplmhi, the reduced number of chro- 

 mosomes is one in one variety and two in another, it 

 has been found by one of Boveri's students that about 

 half the embryos contain one more chromosome than the 

 other half. This chromosome is attached to one of the 

 others in the early stage and hence does not appear as 

 single. 



This discovery shows that even when no accessory is 

 found it may still be a part of one of the other chromo- 

 somes — and being confined to one sex fulfills all the con- 

 ditions of the sex mechanism. 



The conclusions arrived at from a study of these uni- 

 sexual animals have been confirmed in the partheno- 

 genetic phylloxerans and aphids. 



Two years ago I found that in the phylloxerans two 

 classes of spermatozoa are present ; one is a rudimentary 

 sperm, and corresponds to the male producing of other 

 insects. The other sperm contains the accessory, and it 

 alone is functional. Hence all the fertilized eggs should 

 be female. This has been known for a long time to be 

 the case. 



The female is the stem-mother of the summer brood 

 of parthenogenetic individuals. Thev all contain the 

 full number of chromosomes and are females. At the 



When the male egg gives off its single polar body one 

 (or two) whole chromosomes lag behind the others (that 

 divide) and are thrown out into' the polar body. Hence 

 this egg contains two less chromosomes and it develops 

 into the male. In the sexual female no such reduction 



