GERM CELLS IN ASCARIS INCURVA 79 



true, however, that non-transference in the male is a char- 

 acteristic of other groups not sex-Hnked. This condition sug- 

 gests that in some cases sexes may differ in regard to the mode 

 of synapsis of all chromosomes. Possibly conditions of more or 

 less intimate union of the parasynaptic threads as observed in 

 Ascaris incurva may be one type of such a differentiation. 



MECHANISM OF THE UNEQIL\L MITOSIS 

 A. Description 



A detailed study has been made of the spindle formation of 

 the first maturation division of the spermatocyte with reference 

 to the light it might throw on the problems of mitosis. 



Many combinations of plasma and nuclear stains have been 

 tried for this purpose, but Heidenhain's haematoxylin alone or 

 combined with bismark brown or magenta, Delafield's haema- 

 toxjdm, and saffranin and light green have proved the most 

 valuable. 



The early stages are similar to those described by Brauer 

 ('95) for Ascaris megalocephala var. bivalens. The centro- 

 somes separate while lying in the nuclear surface (fig. 36), move 

 to opposite poles, and the astral radiations increase. Spindle 

 fibers then form and penetrate the flattening nucleus and 

 the chromosomes become arranged in the metaphase plate 

 with the X-group centrally located (fig. 37), and bound together 

 by linin fibers. Figure 37, an optical section through the axis 

 of a metaphase spindle, shows the attachment of the spindle 

 fibers. From left to right there may be seen: an autosome 

 bivalent, two univalents of the X-group, the long X-component 

 with the Y above its right end and lastly in the background 

 an autosome bivalent. The attachment of both sex-chromo- 

 somes and autosomes is precisely the same; each chromosome 

 is attached at either side to pairs of fibers from opposite poles. 

 The long X-component and the Y are attached as if the group 

 were composed of a bivalent autosome (the Y and the end of 

 the long X opposed to the Y and a univalent, the unopposed 

 end of the long X-component) — that is each of these two units 



