THE MATURATION DIVISIONS IN ASCARIS INCUR VA. 149 



cyte divisions should be of two classes, one showing 21 chromo- 

 somes including the microsome, and the other 14. Examination 

 of numerous metaphase plates has proved this in the clearest 

 manner to be the case (Figs. 9 and 10). This condition may be 

 compared with that in Ascaris lumbricoides in which the two 

 classes of secondary spermatocyte cells show respectively 19 and 

 24 chromosomes, or with Acholla multispinosa in which the 

 spermatids receive either 11 or 15 chromosomes. 



Oogonial cells showing division figures have not been found 

 but the constant presence of 21 chromosomes in the maturation 

 divisions of the egg indicates most certainly that the diploid 

 number in the female is 42. Metaphase and anaphase plates 

 of the first oocyte division repeatedly give the count of 21 

 chromosomes. Figs. II and 12 show two daughter plates found 

 superimposed within a single section and each gives the count 

 of 21 chromosomes including the microsome. Such an observa- 

 tion of the dividing microsome, together with its constant 

 behavior as a member of the X-group in the spermatocyte cells, 

 gives the conviction that this minute body is in reality a chromo- 

 some. The second oocyte plates (Fig. 13) again reveal the 

 expected count of 21 chromosomes of which one is the microsome. 

 Side views of both oocyte anaphases show a clean separation of 

 daughter plates with no sign of lagging chromosomes, so con- 

 spicuous in the first spermatocyte division. 



These results demonstrate that in Ascaris incurva there are 

 formed two classes of spermatozoa, one bearing 21 chromo- 

 somes, the other 14 chromosomes; and they indicate that 

 fertilization of the egg carrying 21 chromosomes by a spermato- 

 zoon of the first class gives rise to the females which have 42 

 chromosomes and by one of the second class to the males which 

 have 35 chromosomes. This cycle of the chromosomes may be 

 summarized in the following formulae in which the aiitosomes 

 are designated as A and the sex chromosomes as X and Y. 



Spermatozoa of Two Classes. Egg. Gamete. 



I3A + 8X + I3A + 8X = 26A + i6X = 42 (female). 



I3A + Y + I3A + 8X = 26A + 8X + Y = 35 (male). 



I would like to express my thanks to Dr. Edwin Linton for 

 advice and aid in obtaining material and to Dr. E. B. \\ilson at 



