168 Harry Lewis Wieman. 



Sections of the late larval testis show that cyst formation has 

 already occurred in the proximal part of the testis, i. e., the part 

 nearest the sperm duct, while in the more distal region they have 

 not yet formed. 



The spindle shape of each lobe persists during the greater part 

 of the larval stage. The first change consists in an increase in 

 diameter, while the length remains practically the same, which 

 results in the production of a pear-shaped body (Fig. Z. B). 

 During the pupal period the growth at right angles to the original 

 axis of the lobe continues, but not equally in all directions, being 

 inhibited at certain points, and producing a structure which in 

 section resembles the hub and spokes of a wheel. The process 

 continues in this manner until the radiating follicles characteristic 

 of the adult are formed (Fig. Y) . 



At the point opposite from where the sperm duct leaves each 

 lobe, a button-like cap exists (Fig. Y. c) in which the cells are 

 very much 3-ounger than in any otlier part of the testis. This 

 region represents the distal end of the embryonic organ, as can be 

 seen from the method of development. 



The epithelial investment covering the organ is at first very 

 loose and does not extend in between the follicles, and when the 

 testes are removed from the body at this time, the delicate epi- 

 thelium falls away and the naked organs are obtained. In late 

 pupal stages, the epithelial cells become more closely applied, 

 and adhering between the follicles, soon produces the appearance 

 characteristic of the adult, in which the folh'cles are separated 

 from each other by a thick layer of these cells. Through increased 

 number of cell divisions and the growth processes accompanying 

 the maturation of the germ cells, the follicles become greatly 

 enlarged and press tightly against the epithelial partition causing 

 the latter to appear as a definite part of the follicle. 



In connection with the early stages in the development of the 

 ovary, the occurrence of amitotic divisions in the primordial germ 

 cells was noted. At a corresponding stage the same phenomenon 

 is to be seen in the testis. Three steps in the process are shown in 

 Figs. 67, 68 and 69, the appearance of which closely resemble 

 Figs. 34 and 35 from the ovary. 



