MARSUPIAL SPERMATOGENESIS 211 



These chromatoid bodies vary in size and in number. During 

 the first meiotic division they are distributed indiscriminately 

 between the two daughter cells. Further than this they have 

 not been traced. 



The Sertoli Cell in Phascolarctus. 



In Phascolarctus the Sertoli cell nucleus is very large 

 (PL 16, fig. 20). It is about three times as large as the nucleus 

 of the primary spermatocyte when it has attained its maximum 

 volume. The nucleus lies at the foot of the Sertoli cell close 

 to the wall of the tubule. The outlines of the cell could not 

 be distinguished. The chromatin of the nucleus is in the form 

 of a coagulum distributed through the nucleus. In the centre 

 of the nucleus there is a clear space surrounding a granular 

 mass. This granular mass is probably formed by the degenera- 

 tion of the nucleolus. 



The cytoplasm of the Sertoli cell contains, usually lying close 

 up against the nucleus, a varying number of refractive, rod- 

 like bodies. These are a constant feature of the Sertoli cell 

 in Phascolarctus, and I found them present in all 

 the material examined by me whatever time of the year the 

 material was obtained. Usually in close association with the 

 rods, a pale yellow, fluffy mass can be seen. This probably 

 consists of deutoplasmic material. This shows up well in 

 sections which have been fixed in cold Flemming before 

 staining with the iron haematoxyhn. 



In some of the outside tubules of the sections, especially in 

 the Flemming-fixed material, instead of the bundle of rods a 

 mass of over-lapping, very pale plates can be seen (PI. 16, fig. 21). 



The rods appear pale yellow in those sections fixed in the 

 Bouin, but often in the Flemming-fixed material are quite 

 black. The rods are found together, lying approximately 

 parallel. They vary in length, some of them consisting of small 

 pieces lying end to end and probably formed by the fracture 

 of one of the longer rods. Although the rods are usually com- 

 paratively straight, in many cases they are seen to possess 

 a very wavy outline. 



