4O J. T. PATTERSON AND LELIA T. PORTER. 



with the haploid number of chromosomes from one having the 



diploid number. 



THE SPERMATOGONIA. 



We have not attempted to follow closely the course of develop- 

 ment of the male gonads in the larva. At the earliest stage at 

 which the larva can be recognized as a male, each testis consists 

 of a solid spherical mass of cells. Histologically, there are two 

 kinds of cellular elements, germ cells and epithelial cells. During 

 the course of further development the gonad elongates, and at 

 the same time cyst formation occurs. This process is completed 

 by the end of the larval period. 



At no time during the development of the gonad does one 

 find any great number of spermatogonial divisions. Four or 

 five mitotic figures are the most that will be found at any one 

 time in a given testis. 



The period of multiplication ends sometime between forty- 

 eight and twenty-four hours prior to pupation. Of the two 

 larval broods mentioned above, the one preserved forty-eight 

 hours before the time of pupation has a few larvae showing 

 spermatogonial divisions, while the one fixed twenty-four hours 

 later has no divisions. 



Fig. i shows a metaphase plate of one of the dividing spermato- 

 gonia. The plate has eight elongated chromosomes, one of 

 which shows the beginning of a longitudinal split. We have con- 

 cluded from a study of all of our material of both males and 

 females that eight represents the haploid number of chromosomes. 



THE GROWTH PERIOD. 



The growth period begins shortly after the cessation of the 

 spermatogonial divisions, and extends through the fourth day 

 after pupation. At the beginning of this period all of the 

 germ cells in a given cyst are in the same stage of development. 

 In section each cell appears wedge-shaped, with its slightly 

 curved base lying against the outer membrane and its apex 

 directed toward the center of the cyst. The apexes of all the 

 cells in the cyst are usually connected by a common mass, which 

 is apparently the remains of the interzonal fibers of the last 

 spermatogonial division. 



