486 



H. L. Wieman. 



Externally the distal end of the lobe is marked by a round cap- 

 shaped depression (fig. 1, d), A section through this region (fig. 8) 

 shows that the cap is composed of (1) an outer layer made up of 

 two kinds of cells, viz., spermatogonia (sp.) that have not been 

 grouped into cysts, and an isolated mass of pale-staining cells 



Fig. 1 Diagrammatic drawing of the lobes of the testis. A, proximal view; 

 B, side view; C, distal view; a, expanded end of the sperm duct, b, 

 at the point where it leaves the testis. This is shown in dotted outlines in B; 

 c, common sperm duct of one side. This unites with its fellow from the opposite 

 side to form the median sperm duct; d, circular depression opposite the opening 

 of the central cavity of the testis into the sperm duct; e, small area or cap of epi- 

 thelial cells corresponding to the expanded end of the base of the terminal thread 

 of the ovariole. 



Fig. 2 Diagram illustrating three stages in the development of the testis. 

 A, middle larva period; B, late larva; C, pupa, in which the position of the degen- 

 erating cells is indicated by the broken lines ;D, transverse section of C in which the 

 degenerating cells fill the central circular area; a, terminal cap of epithelial cells; 

 b, sperm duct; c, degenerating cells. 



(ex.); (2) an inner layer of degenerated cell fragments (d), which 

 is definitely marked off from the spermatogonia above and the 

 spermatozoa below by a delicate capsule of thin flattened epithe- 

 lial cells (e.m.). It is with the history of the peculiar cytologica 



