REDUCTION DIVISION 377 



cell, growing, forms a primary spermatocyte. At the end of the 

 growth period the primary spermatocytes, one after another, divide 

 transversely, i.e., at right angles to the nema's body axis, and then, 

 sometimes almost simultaneously, longitudinally, to produce four simi- 

 lar, juxtaposed spermatids (Fig. 2, qrt), each soon packed with several 

 thousand very slightly elongate microsomes, nearly all of which are 

 located outside the large central, faintly alveolated, diminishing nuclear 

 space. (Fig. 2, micrsm and alv ncl; and Fig. 14.) 



The microsomes seem to arise toward the center of the spermatid 

 and migrate outward till the entire cell is colonized by them. Seen 

 toward the center of the spermatid they usually have their long 

 axes arranged radially, as if moving outward, end on. Some 8- 

 10,000 uniform microsomes come thus into existence in each sperma- 

 tid. The arrangement of these around 64 centers is the first indica- 

 tion of the formation of the first generation of 64 spermatidia. In 

 the living spermatids the microsomes are the only objects seen 

 visibly connected with such a division of the cell contents as is 

 necessarily postulated to account for the phenomena of heredity. 





l 



Fig. 3 Fig. 4 



Fig. 3. View near blind end of testis of S. parasitifera, showing pairs of cells result- 

 ing from division of primordial nuclei. This testis had broken open and become par- 

 tially evacuated so that these pairs of cells in tandem could readily be distinguished as 

 such. Normally these nuclei are so packed that the mass effect obscures the fact 

 that they are twins. 



Fig. 4. Second stage of reduction division of a spermatocyte of S. parasitifera, 

 which will result in 4 similar juxtaposed spermatids, as at qrt, Fig. 2, each having 7 

 chromosomes. The compound chromosomes present considerable individuality. 

 Between the 2 double groups of chromosomes is seen portion of the new cell wall. 

 X 1200. 



In the first of these two divisions the chromosome number is re- 

 duced to seven. Probably the smallest one of the seven chromosomes 

 of the secondary spermatocytes differs slightly in relative size in the 

 two cells. Thus far the spermatogenesis presents nothing very new 

 or striking, but the amount of growth, from 3 to 60 microns (tst, 

 Fig. 2),- is worthy of note, and, connected with reduction, there is 



