402 CHARLES H. SWIFT 



In this, and the next stage to be described, the position of 

 the peritoneal cells is also of great interest. In general there 

 are one to three of them between adjacent spermatogonia and 

 their long axes, too, are at right angles to the long axis of the 

 cord (figs. 5 and 6). Their nuclei are placed next the basement 

 membrane, while most of the cytoplasm is towards the central 

 axis of the cord or tubule (figs. 5 and 6). This is the reverse 

 of the condition in the spermatogonia. 



In this stage and in the next we begin to have an idea of what 

 obtains in the adults which have been studied. The spermato- 

 gonia at the basement membrane of the tube and between them 

 the supporting cells — cells of Setroli — which are derived from 

 the peritoneal cells. 



In the next stage — a 3 day chick — the stroma is greatly re- 

 duced in amount as are the interstitial cells also. Most of the 

 testis is taken up by the seminiferous cords and tubules, which 

 are arranged in the way described in the 20 day chick embryo. 



Most of the seminiferous cords have by this time acquired a 

 ca\dty and may now be called tubules. In these seminiferous 

 tubules nearly all the speniiatogonia are against the basement 

 membranes, as described before (fig. 6). The peritoneal cells 

 have lengthened, or been pressed out, so that they begin to look 

 like the supporting cells of an adult seminiferous tubule (fig. 6). 

 In this as well as in the last stage, the spermatogonia are occa- 

 sionally seen dividmg (fig. 6). In these rare cases the mitotic 

 figure is arranged, not like that which gives origin to the sper- 

 matocyte, but so that the line of cleavage between the daughter 

 cells is at right angles to the long axis of the seminiferous tubule 

 (fig. 6). In this way both daughter spermatogonia are kept 

 in their proper position, next the membrane, and the number of 

 peritoneal cells, or cells of support, which is still too large, is 

 reduced by pressure (fig. 6). 



In the 6 and 10 day chicks there are no changes of any mo- 

 ment to record, except that there is a progressive increase in the 

 size of the lumen of the seminiferous cords and a reduction in 

 the amount of stroma and in the number of interstitial cells. 

 The cavity in the seminiferous cord, even at 10 days is slit-Uke 



