404 CHARLES H. SWIFT 



There are, then, two main opinions held as to the origin of the 

 interstitial cells; the one school, including Kolliker, Tourneux 

 (79) and Plato ('97), hold that they arise from the connective 

 tissue cells; the other group, to which belong Niissbaum ('80) 

 and von Bardeleben, believe that they come from the general 

 epithelium. Allen ('03) and Whitehead ('04) must be classed 

 as holding the latter, and Sainmont ('05) the former opinion. 



In the male chick embryo the interstitial cells are first evi- 

 dent in the 13 day testis. They are not numerous and are 

 evenly scattered throughout the testis. Usually they appear as 

 single cells but at times 2-6 may be found together. The cells 

 themselves have various forms, sometimes cubical, sometimes 

 polyhedral and frequently fusiform. The nucleus is round or 

 oval, stains deeply and usually has a central position (fig. 5). 

 The cytoplasm of these cells also stains strongly and appears 

 dense (fig. 5). The interstitial cells are remarkable, however, 

 because of the immense amoimt of fat which they contain. 

 This fat in the stained specimen has been dissolved out, but the 

 vacuoles, which contained it are present, and occupy no small 

 part of the cytoplasm (fig. 5). If the section be examined care- 

 fully intermediate stages between the connective tissue cells 

 and the interstitial cells can be seen. That is, certain of the 

 connective tissue cells will be seen containing small vacuoles and 

 arranged at times in small groups. 



In the 15 and 17 day embryonic testes there is an immense 

 amount of interstitial cell tissue. It is arranged in masses and 

 cords of vaiying sizes between the seminiferous cords. The in- 

 terstitial cells of these and later stages can be easily seen before 

 the section is stained and while it is still in paraffin. The inter- 

 stitial cell cords and masses, owing to the contained fat, stain 

 black with osmic acid and hence show up dark against the 

 lighter background. Sainmont ('05) described a rich plexus of 

 capillaries in relation to these masses of interstitial cells in the 

 cat, but in the chick there seems to be no increase in vascularity 

 around them. 



Beginning with hatching and continuhig until the chick is 10 

 days old there is a progressive decrease in the amount of inter- 



