3OO J. E. WODSEDALEK. 



3. Reduction Division. 



Nineteen chromosomes appear in the late prophase or early 

 metaphase stages of the primary spermatocyte (Figs. 15-18). 

 Eighteen of these are the ordinary chromosomes or autosomes 

 and the other is the accessory chromosome. The accessory in 

 this case is practically always found outside of the main mass of 

 chromosomes, either in close contact with them (Figs. 16 and 18), 

 or a short distance away (Figs. 15 and 17). The large size of the 

 eighteen autosomes which are about four times the size of the 

 chromosomes in the spermatogonia indicates that they were 

 formed by the growth and pairing of the thirty-six autosomes 

 found in those cells, while the accessory remains unpaired, making 

 a total of nineteen. 



In these cells as in the case of the spermatogonia the chromo- 

 somes are frequently bunched together, making an accurate 

 count difficult and often impossible. However, mitotic stages 

 particularly of the first and second spermatocyte divisions were 

 very numerous and among the thousands of cells in mitosis 

 examined several hundred definite counts were made. Figs. 

 19-29 show the accessory in characteristic positions in the meta- 

 phases of division of the primary spermatocyte. The heart- 

 shaped body always passes toward one pole in advance of the 

 other chromosomes and frequently may be found at the pole 

 before the other chromosomes have divided (Figs. 28 and 29). 

 The chromatoid body which is spherical in shape and much 

 smaller than the accessory is also invariably present and very 

 conspicuous. As a rule it is in the spindle, and in a large ma- 

 jority of the cases goes in the direction opposite from the accessory 

 (Figs. 21, 22, 23, 24, 25, 27 and 28), though this behavior is by 

 no means constant, for occasionally it is found with the accessory 

 on the same side of the equatorial plate (Figs. 20, 26 and 29). 



When the large, apparently quadrivalent chromosomes divide, 

 the resulting chromosomes are somewhat larger than the chromo- 

 somes of the spermatogonia. Immediately after the chromo- 

 somes divide they unite in twos (Fig. 29) so that at the time of 

 their arrival at the poles they do not number eighteen, but only 

 nine or exactly one half that number (Figs. 30-35). Additional 

 proof that such a second pairing of the chromosomes occurs lies 



