E. H. Whitehead 179 



power of the microscope at my command, the sphere contains no radia- 

 tions, though sometimes there are a few minute grains in the clear space 

 aronnd the central body. The latter, as was said, is much larger than 

 that of the first sphere; it is not homogeneous, but seems to l)e consti- 

 tuted by an aggregation of granules. Its outline frequently is circular, 

 but often it is irregular and its periphery uneven, and its size is variable. 

 This sphere is almost always at some distance from the nucleus, though 

 when it alone is found in a cell, it may be near the nucleus. The central 

 bodies of both spheres stain with iron-hsematoxylin ; also Mallory prepa- 

 rations show them quite clearly, and they are readily made out in un- 

 stained sections of Flemming material. The great majority of Leydig's 

 cells seen in the early stages present one or the other of these structures, 

 and a great many of them show both at the same time, so many, indeed, 

 that I think both may be regarded as normal constituents. Their mor- 

 phology, staining reactions and constancy make it possible that both 

 are centrospheres, and I shall call them such. The point, however, 

 which I should like to emphasize is that the first structure — the large 

 sphere with the small centrosome — is not permanent, but soon disap- 

 pears; it could not be found in embryos of greater length than 3 cm. 

 The second centrosphere, however, persists, and is found in all the suc- 

 ceeding stages of embryonic development (Figs. 3, 4, 8) ; even in the 

 atrophied cells of the pig at 14 cm. they still can be demonstrated. In 

 the later stages, however, the centrosome often seems smaller, more 

 homogeneous, and more regularly circular in outline (Fig. 8) ; the 

 sphere is usually smaller and its wall more homogeneous in appearance, 

 so that the whole structure somewhat resembles a vacuole with a hyaline 

 content. 



The Occurrence of Fat. — The occurrence of fat in the seminal tubules 

 and Leydig's cells of various mammals has been noted by several ob- 

 servers. Allen (loc. cit.) bases a theory upon the presence of fat in the 

 primitive seminal tubules and germinal epithelium, suggesting that fatty 

 degeneration of these cells may furnish a "stimulus or condition which 

 brings about the formation of the interstitial cells." 



For the study of this subject I used material fixed in Flemming's 

 solution, employing unstained sections as well as sections stained with 

 iron-hfematoxylin. Owing to the doubts which have been raised as to 

 the reliability of osmic acid as a test for fat, the results thus obtained 

 were controlled by frozen sections stained with Sudan III. In the 

 germinal epithelium of pigs from 3 cm. to 4 cm. it was not possible to 

 demonstrate any fat with either osmic acid or Sudan III. In all these 



