A Cytological Study of the Scnii-parasitic Copepod, Hersilia apodlformis etc. 437 



jthe Constitution of the resulting spermatozoa? The various possibilities 

 are diagremmatically given in Textfigure /. Above, right and left, are 

 represented the somatic chromosomes of the male and female: the allo- 

 somes by foiir (black) chromosomes with "Querkerbe", the hetero-chromo- 

 somcs by circles. As in the Insecta, the female is assumed to contain two 

 hetero-ehromosomes of like composition, i. e. two x-chromosomes (circles 

 with Grosses); the male, two hetero-ehromosomes of unlike composition, 

 one x-chromosome and one y-chromosome (piain circle). 



In the metaphase of the first spermatocyte would be two di-tetrads 

 and two hetero-ehromosomes. At the left of Figure I is shown the normal 

 first spermatocyte anaphase: the x-chromosome passes to one second 

 spermatocyte, the y-chromosome to the other. A normal metaphase of the 

 two sister second spermatocytes is shown below this. The division of these 

 gives rise to two classes of spermatozoa, those containing an x-chromo- 

 some, class a, and those with a y-chromosome, class h. If, however, as 

 described on page 49, one of the hetero-ehromosomes lags behind in the 

 anaphase of the first spermatocyte mitosis, and the line of division of 

 the cytoplasm into second spermatocytes passes through it, it becomes 

 attached to the two metaphase plates of the second spermatocytes. There 

 are two possibilities, since both hetero-ehromosomes usually lag (Fig. 31, 

 Plate VI), either that the y-chromosome or that the x-chromosome 

 is halved. The first possibility is represented above (1, Fig. /) ; the second, 

 below (2, Fig. I). To the left of the middle line are the metaphase plates 

 of two sister second spermatocytes; in the middle (below the numerals 1 

 and 2), the telophase stages and the four resulting spermatids. These 

 form four classes of spermatozoa. In both cases 1 and 2 are alike, classes a 

 and h are normal, while the + class contains two hetero-ehromosomes 

 and the — class has no hetero-chromosome. The latter class has little 

 significance as the spermatids would be likely to degenerate, as those 

 without hetero-chromosome in Rhabditis (Boveri, '11 ; Schleif, '11) and 

 Aphis (Baehr, '09). It is the -f class, with both an x-chromosome and 

 a y-chromosome, which arouses interest. Should such a spermatozoan 

 fertilize a normal egg (right, Fig. 7), the resulting individual (middle, Fig. I) 

 would contain two x-chromosomes and one y-chromosome. Thus it would 

 possess the sex determinants necessary to produce a female (2 x) and 

 those necessary to produce a male (x + y). Considering the y-chromatin 

 as an Inhibitor to the production of female characters (the determiners 

 for maleness, being more probably in the autosomes), its presence in the 

 hermaphrodite might account for the fact that only the male secondary 

 sexual characters appear in the soma. 



