458 N. M. Stevens 



first division gives, or may give, in the same individual six differ- 

 ent kinds of second spermatocytes with reference to this chro- 

 mosome {s), while there are, as usual, two kinds with reference to 

 the large heterochromosome (x). If the small chromosome goes 

 undivided to the same pole with the odd chromosome (x) (Fig. 33), 

 we have second spermatocytes containing nine and eleven chro- 

 mosomes (Figs. 40 and 41); if it goes undivided to the other pole 

 (Figs. 31 and 37), the resulting second spermatocytes each contain 

 ten chromosomes, one showing the large the other the small hete- 

 rochromosome (Figs. 42 and 43); while if it divides, the second 

 spermatocytes contain ten and eleven chromosomes (Figs. 44 and 

 45). As might be expected one finds two conditions in the second 

 spindle. Either a small daughter chromosome is found outside 

 of the equatorial plate (Fig. 46), or the small chromosome which 

 has not divided in the first division, divides in the second (Fig. 47). 

 Both conditions may be found in the same cyst. It is, of course, 

 in only a few favorable spindles that it is possible to see the small 

 chromosome actually dividing, but the metaphases are readily 

 separated into two classes, one where all of the chromosomes are 

 in the equatorial plate (Fig. 48) and another in which one small 

 chromosome, which from its form and size is evidently a daughter 

 chromosome from the first division, appears outside of the plate 

 and often quite near one pole (Fig. 46). It is therefore quite cer- 

 tain that the small heterochromosome divides in either the first 

 or second division but not in both. Clear daughter plates of the 

 second division have never been found. 



The conditions described above lead to the production of two 

 equal classes of spermatozoa with reference to the large hetero- 

 chromosome (x) and four classes, which may be quite unequal, 

 with reference to the two heterochromosomes. 



Equal numbers < 



I 



N , / variable numbers. 



II ^ > variable numbers. 



[9 + X + s 



