The Chromosomes in Diahrotica 459 



If J always went to the same pole with x in the first division the 

 classes of spermatozoa would be as follows: 



Equal numbers < ,, ^ 

 ^ UI 9 + ^ + -f 



If s always went to the opposite pole from x, we should get the 

 following results: 



T? 1 u f I. Q + J- 



Equal numbers s ^t 



^ [11. '9 + X 



If J- always divided in the first spermatocyte division, there would 

 be four equal classes of spermatozoa: 



Equal numbers \ 



T J ^ ,1 equal numbers. 



' ^^9 + . j ^ 



11 < ^ > equal numbers. 



19 + X + J- J ^ 



A study of seventy or more individuals of this kind gives the 

 impression that the small heterochromosome most often divides 

 very late in the first division, but it is certain that there is consider- 

 able individual difference. In some cases nearly every anaphase 

 of the first division shows s dividing; in others, it is rarely or never 

 seen dividing in the first spindle, and as stated above, all of the 

 various possibilities have been found in one individual. 



Type lib ' 



Fifteen out of the same 100 males of Diabrotica soror had two 

 small heterochromosomes in addition to the eighteen ordinary 

 chromosomes and the large heterochromosome x. These are 

 shown in a spermatogonia! plate (Fig. 49). The three hetero- 

 chromosomes may also be seen in a growth stage (Fig. 50), a 

 prophase of the first division (Fig. 51), lateral and polar views of 

 the metaphase (Figs. 52 and 53) and an anaphase (Fig. 54). 

 Fig. 55 is an equatorial plate of the second division. When 

 two small heterochromosomes are present both may go to either 



