INTERSTITIAL CELLS OF TESTICLE IN DIDELPHYS. 179 



mals (rat, guinea-pig, rabbit, dog and man) Ciaccio (1910) de- 

 scribes a number of granules and vesicles which, after fixation 

 with his special methods, stain with Sudan. Ciaccio considers 

 these bodies as formed by a lipoid substance which, in his 

 opinion, has a great analogy to the substance of the chondrio- 

 somes. Although none of my material was fixed exactly accord- 

 ing to Ciaccio's prescription, I applied his method of staining to 

 material fixed in Regaud's fluid and subsequently kept in 3 

 per cent, bichromate for a week, a procedure which is similar 

 to Ciaccio's method I. The results were identical with those 

 obtained from preparations fixed with reagents containing osmic 

 acid; that is to say, Sudan apparently stained in red what 

 would be stained black in osmic acid. This conclusion was 

 reached through the study of the seminal epithelium, in which 

 the fat droplets have a characteristic arrangement, rather than 

 through the study of the interstitial cells in which no such regular 

 arrangement exists. 



Pigment, which has often been found in other mammals and 

 quite lately in the woodchuck by Rasmussen (1917), does not 

 appear to exist at all in the interstitial cells of the opossum. 

 Crystalloids, on the other hand, are found in many cells and are 

 of two types. So far, those described for the first time by 

 Reinke (1896) are supposed to exist only in human material, 

 although Mathieu (1898) mentions the presence of "filaments 

 cristalloidiens" in the interstitial cells of the testicle in the cat. 

 The plates accompanying his paper, however, are by no means 

 clear. In the opossum many interstitial cells contain bodies 

 similar to Reinke's crystalloids, although smaller and not so 

 abundant (Fig. 6). They appear most clearly after fixation 

 with Benda's or Meves' fluid, and can be seen in all other material 

 except that fixed with Regaud's reagent; after the application 

 of Benda's method they usually stain in brown. These bodies 

 are rather short and thick; their ends are not pointed but blunt. 

 Frequently they appear to be formed of two substances a 

 darker peripheric, and a lighter central one. In most cases only 

 one crystalloid is found in a cell; occasionally, however, their 

 number is increased, although they are never so abundant as 

 Reinke's crystalloids in man. Sometimes a large crystalloid 



