SPERMATOGENESIS IN THE ALBINO RAT 



167 



occurs in the Wistar rats throughout the process of spermato- 

 genesis. Hewer records the first appearance of a lumen in the 

 tubule at seven weeks. My figure 5, which is typical of all the 

 individuals studied of about 14 days of age, shows the lumen 

 present. Hewer's material did not differentiate first sperma- 

 tocytes from spermatogonia until three and a half weeks after 

 birth. Mine shows this differentiation as far as the pachytene 

 stage at two weeks. 



In this connection the following data with regard to the con- 

 dition of the young rats which I studied will be of interest. 

 With the exception of rats aged 14 and 16 days, the individuals 

 were under weight, as shown in table 1, a fact which would not 

 favor precocity, but rather retardation of development. 



TABLE 1 



The figures in the first two colums are taken frorn Do7ialdson's {'IS) tables. The 

 third column is the weight of the rats used in this study, of age correspondi7ig to 

 column 1. The last two columns show the associated cell activities 



AGE IN DAYS 



10 



11 



12 

 13 

 14 

 15 

 16 



BODr WEIGHT IN 

 GRAMS, STANDARD 



13.5 

 13.9 

 14.4 

 14.9 

 15.5 

 16.1 

 16.7 



MOST ABUNDANT CELLS 



Type A • 

 Types A and B 

 Type B (slight) 

 Types A and B 

 Types A and B 

 Types B and C 

 Types C and D 



MOST ADVANCED 

 CELLS 



Pachytene 



TypeB 



Type B 



Leptoterie 



Pachytene 



Pachytene 



Diplotene 



The study of this series of young testes shows that the differ- 

 entiation of the spermatocytes from the indifferent cells of type 

 A (figs. 2 to 15) is a process which, in the early stages, involves 

 all the tubules of the testis, and to an extent very nearly equal 

 in each tubule, although at any given age in days the stage reached 

 may vary somewhat. The change from this generally similar 

 condition of all the tubules to that of the differential activity in 

 parts of the tubule characteristic of the adult testis is a gradual 

 one. 



In the early stages the degree of variation in individuals of 

 nearly the same age is not great; e.g., in rat no. 150, 10 days old, 



