THE PROBLEM OF SEX DETERMINATION. 159 



has become embedded or attached to its nuclear wall, so that ultimately 

 the nucleus of each primitive ovum is seen to be composed of one part 

 derived from the spermatozoon, and the other part the female portion. 

 These two elements of the nucleus never fuse, but retain their indi- 

 viduality throughout all the oogonial divisions. The double nucleus 

 divides amitotically, each half separately. In the majority of the 

 divisions the male and female portions of the nucleus divide equally, 

 so that a similar quantity of nuclear material, both male and female, 

 gets into each daughter cell. There are probably about forty to fifty 

 oogonial divisions in all. In these the male and female portions 

 of the nucleus divide and move apart simultaneously, the male 

 portion usually dividing first. Now and again, however, the female 

 half of the nucleus seems to divide before the male portion, so that 

 the male portion gets left behind and is shut off entirely in one 

 of the daughter cells. Therefore of the two resulting cells of this 

 division, one has the whole of the male part of the original nucleus 

 and its share of the female portion, while the other has only half the 

 female and no male substance. This appears to be the sex determining 

 factor ; for of these two daughter cells, the one that has received the 

 whole of the male element, plus the female element, becomes the 

 female, while that which has received the female portion alone be- 

 comes the male. Both these kinds of eggs, once the sex determining 

 division has taken place, grow rapidly. They seem to accomplish this 

 through the power of absorbing and building up into themselves all 

 the other immature egg cells with which they happen to come in 

 contact, and in which the divisions of the two portions of the male 

 and female substance has been equal. The outcome of this process is 

 that the male egg is not fertilized, while the female egg is. It is, how- 

 ever, impossible to speak in the strict sense of the word of the male 

 egg as unfertilized, as it has been directly under the influence of the 

 sperm in all the early oogonial divisions previous to the sex deter- 

 mining one. For all the primitive germ cells are joined in the 

 first place by a spermatozoon, irrespective of the fact that only 

 some of these will give rise to ova later, and that the majority will be 

 only nurse cells. It is only in the late stages, shortly before the female 

 egg is laid, that the two portions of the nucleus, the male and 

 female actually fuse beyond recognition. As the two kinds of eggs, 

 male and female, are not found in a simple ratio, but in the proportion 

 of three or two, to one male, it is probable that some other division 

 takes place in the case of tlie female egg. I have been unable to 

 decide this point so far, from my sections. 



I have made a careful study of the maturation divisions, and as Kor- 



