PREDETERMINATION OF SEX 293 



When the polar body is thrown off all of the chromosomes divide. 

 The migrant that develops from this egg comes to produce large 

 eggs with the full complement of chromosomes in them. All of 

 the chromosomes divide when the polar body is produced by this 

 egg (plate 1, fig. n). The egg itself then develops into the sexual 

 female that comes to produce a single egg. When this egg is 

 ripe the chromosomes have united in pairs, of which there are 

 three. In reality one of these pairs must be thought of as made 

 up of the two large sex chromosomes and the two small chromo- 

 somes attached to them. 



If we next turn to the line represented on the right of the dia- 

 gram we see that the stem-mother contains the same group of 

 chromosomes as in the other case (one of the small sex chromo- 

 somes is marked). All of the chromosomes divide when the 

 polar body of the egg of the stem-mother is given off. The egg 

 gives rise to the migrant that comes to produce the small eggs. 

 When the polar body is about to be produced in these small 

 eggs (or before that event) a shifting of the sex chromosomes 

 takes place, so that the two large X's come together as do the 

 two small ones, the latter leaving their former loose attachment 

 to the large chromosomes in order to combine. When the polar 

 body is given off the four autosomes divide, while the conjugated 

 pairs of sex chromosomes separate; a member of the larger pair 

 lags on the spindle and is precociously split lengthwise, while 

 the small pair separate and the outer member does not lag on 

 the spindle (plate 1, fig. o). It will be seen that two kinds of 

 eggs should result according to whether the marked chromosome 

 passes out into the polar body, or remains in the egg. If it 

 passes out, the male that results will give rise, as shown in the 

 figure, to female producing spermatozoa that contain the open 

 x. If we suppose the sexual egg is fertilized by this kind of 

 spermatozoan, the stem-mother that results will give rise to the 

 female line (to the left). If we suppose that the other kind of 

 sperm — the one with the marked x — fertilizes a sexual egg, a 

 stem-mother will be produced that leads to the male line (to the 

 right). The assumption that there are two kinds of males is 

 not entirely hypothetical; for, in my former paper I pointed out 



