486 ANDREW T. RASMUSSEN 



RESULTS 



In late August, September and October the testes of the adult 

 woodchuck are minimal in size, being only 0.015 per cent to 0.020 

 per cent of the reduced body weight. They are abdominal, oc- 

 cupying a variable position in the dorsal portion of the abdom- 

 inal cavity on a level usually with the upper two sacral verte- 

 brae. They are a chocolate brown in color, due to a dark yellow 

 pigment found in the interstitial cells. The relative amount of 

 interstitial tissue may be judged from figure 1, which, however," 

 is taken from an animal killed much later in the year. This 

 tissue is so loose that if an entire testis is placed in Carnoy's 

 fluid the organ collapses from the absorption of the lymph faster 

 than the fixer enters the dense connective tissue tunica. It 

 consists of a fine connective tissue framework in which, be- 

 sides the usual fixed connective tissue nuclei, blood and lymph 

 vessels, etc., there are found a number of interstitial cells of 

 Leydig varying in size from small cells about 5 ix in diameter, 

 with practically no cytoplasm and a more or less vesicular nu- 

 cleus, to larger cells about 10 ix in average diameter, with a 

 fair quantity of cytoplasm usually containing pigment granules, 

 which are slightly more numerous early in this period than later. 

 The nuclei of some of the smaller cells may be somewhat irregu- 

 lar or slightly spindle shaped and resemble the fixed connective 

 tissue nuclei. Indeed it is practically certain from the investi- 

 gations upon the origin of these cells that they are of connec- 

 tive tissue origin, and it is not improbable that they may re- 

 turn to this type again. The nucleus, however, of most of these 

 interstitial cells has the oft-described spherical and vesicular 

 appearance containing one nucleolus and a chromatin network 

 which' is especially coarse next to the nuclear membrane. The 

 cytoplasm varies greatly in amount, although it is always scanty 

 at this stage and gives a variety of irregular shapes to the cells, 

 as may be seen from figure 2 and the smaller cells in figure 3. 



In nearly all these cells there are a variable number of the 

 small brown or dark yellow pigment granules. These, while 

 undoubtedly derived from the very labile lipoid or fatty glob- 



