TESTICLE AS GLAND OF INTERNAL SECRETION 495 



notable increase and the interstitial cells become flattened out, and due 

 to the rapid growth of the spermatogenic cells they are relatively less 

 abundant. In regard to number, the number of interstitial cells is sup- 

 posed to diminish from embryonic life to birth when there is a cessation 

 and finally just before puberty there is a rapid increase in the number 

 of interstitial cells. 



Loisel in some of his work on the testicles of poultry brings out the 

 fact that there are two kinds of interstitial cells, one formed from the 

 connective tissue cells and producing colored pigment and the other a true 

 sexual cell formed from the same embryonic element that forms the sper- 

 matogenic tubules and produces a clear secretion. These are the true 

 sexual interstitial cells. 



In a typical interstitial cell it will be noted that there is a more or 

 less eccentrically placed mass of condensed granular cytoplasm contain- 

 ing the nucleus; while the peripheral portion of the cell is extensively 

 vacuolated. So marked is this arrangement that one can speak of endo- 

 plasm and ectoplasm. By no means all of the cells have this typical struc- 

 ture, but all gradations are found from cells whose bodies are composed 

 entirely of "endoplasm," to those in which it is reduced to a remnant in the 

 immediate vicinity of the nucleus. The vacuolated forms are regarded 

 as old cells by some, the opposite extreme being youthful forms ; whereas 

 others think that this appearance is a secretory phenomenon connected 

 with the production of fat. The analogy with what has been observed in 

 various gland cells is certainly very suggestive of secretory function. The 

 vacuoles are not always smooth and regularly circular ; frequently they 

 are large, irregularly shaped cavities with more or less ragged margins, 

 doubtless the result of the breaking down of the partitions between adjacent 

 vacuoles. 



The nucleus is relatively large, and contains much nuclear sap with 

 a large nucleolus. It is almost always eccentric in position and poly- 

 chromatic to stains. The finding of mitotic figures in the interstitial 

 cells is rare but some investigators report finding a very few mitotic fig- 

 ures in very fresh material derived from executed criminals. Evidence of 

 karyokinesis is rarely seen in these cells except in the early stages of their 

 embryonic development. It is possible that they multiply by direct di- 

 vision as one occasionally sees two nuclei in a cell and practically never 

 mitoses. 



Cell Contents. I. Fat. As so much importance has been attached by 

 various authors to the existance of fat in these cells, a special study of 

 it should be made. Fat is found in the interstitial cells and in the sper- 

 matogenic tubules in all of the common animals except the pig and the 

 oppossum. 



The arrangement of the fat in the cells is interesting. It is de- 

 posited as small globules which, however, may fuse into larger mulberry- 



