THE SPERMATOGENESIS OF UMHRA LIMI. 127 



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may be arrived at by counting the number of spermatogonia in a 

 cyst which is ready for the first maturation division. On such a 

 basis there are at least six generations. 



The cells of the late multiplication period are usually so small 

 and the chromosomes so massed that counts of the chromosomes 

 are not satisfactory. In so far as counting can be done the 

 numbers check with those obtained in the earlier cells where 

 counts were possible. Although twenty-two chromosomes may 

 be observed it is practically impossible to identify homologous 

 chromosomes in these cells. 



Turner ('19) describes in the perch a nuclear contraction of 

 the transforming spermatogonia accompanied by the extrusion of 

 liquids or particles into the cytoplasm. In Umbra no such 

 phenomena occur. In all spermatogonial mitoses a definite 

 centrosome appears at each pole of the spindle. The early 

 spermatogonia of the spermatogonial growth period (Fig. 2) are 

 from three to six times as large as the resultant spermatogonial 

 cells of the last multiplication (Figs. 15 to 17) division. For 

 example; the average early growth-cells range in diameter from 

 31.20 micra to 66.30 micra, while late spermatogonial cells which 

 are ready for the first maturation division, have an average 

 diameter of about 19.50 micra. While there are minor exceptions, 

 the majority of the cells in the different cysts are approximately 

 of the same size just before the first maturation division. This 

 and the succeeding divisions are very rapid in Umbra. This is 

 probably true in most of the Teleosts, and may be the reason 

 why so many investigators have found difficulty in finding the 

 various stages in fish spermatogenesis. It is necessary to cut and 

 examine a very large number of sections in order to find the 

 proper stages. In this study over five hundred slides were made 

 and examined. 



THE FIRST MATURATION DIVISION. 



I. Growth of the Primary Spermatocyte. At the time of the 

 transformation of the spermatogonia of the last multiplication 

 division (Figs. 15 to 17) into primary spermatocytes the spermato- 

 gonial cells may show one to three deeply staining chromatin nuc- 

 leoli. The nucleoli apparently separate into chromatin granules. 



