400 Experimental Zoology 



pole and the other half to the other pole, and the second polar 

 body is formed (Fig. 6). Thus while the first division is a di]- 

 jerential division, the second is an equation division. It is 

 supposed, also, that in some eggs the above order is reversed, 

 and the first division is an equation division, and the second 

 a differential one. The end result is the same in both 

 cases. 



An exactly parallel series of events takes place in the formation 

 of the spermatozoon. The early sperm-cells, the spermato- 

 gonia, contain the full number of chromosomes. These pair, as 

 in the egg, and two cell divisions take place later, — one a differ- 

 ential, and the other an equation division. In the case of the 

 sperm-cells, however, all four cells become functional sperma- 

 tozoa, while in the egg the polar bodies do not develop. The 

 first polar body often divides. The three polar bodies and the 

 egg are equivalent to the four spermatozoa. 



What support do these results give to the hypothesis that sex 

 is determined at one or at both of these divisions ? The facts 

 so far stated furnish no real support for this idea, since the 

 differential division merely separates a paternal from a maternal 

 chromosome ; and if we do not confuse paternal with male pro- 

 ducing, and maternal with female producing, there is nothing in 

 the facts, as I have said, that supports the idea that this division 

 is a sex-determining one. In regard to the equation division, 

 the observations show that the chromosomes split into exactly 

 Hke halves, and there is also nothing here to support the idea 

 that one half is male and the other half female determining, 

 for this division resembles, outwardly at least, all other equation 

 divisions of the body-cells that are supposed to produce equiva- 

 lent parts. 



If this were the only evidence we possessed in regard to. the 

 maturation divisions, it would lend no support to the hypothesis 

 that the sex of the egg or of the sperm is determined at this time ; 

 but there are some recent observations showing that in a few 

 groups two kinds of spermatozoa are formed, so far as their 

 chromosomal contents is concerned, and we must now examine 



