CYTOPLASMIC STRUCTURES IN THE SEMINAL EPITHELIUM OF THE OPOSSUM. 51 



immersed on 0.1 percent gold chloride for 2 to 3 hours; then in hyposulphite for 

 20 to 30 minutes. The results were excellent. Probably any nuclear dye could be 

 used as counter stain. I resorted to Ehrlich's hematoxylin, to safranin, and to 

 methyl green (Cowdry, 1916), which in the concentration of 0.5 per cent, applied 

 for 30 to 60 seconds, gives a very sharp constrast with the black color of the appara- 

 tus and the pale background. 



SHORT SURVEY OF THE PROCESS OF SPERMATOGENESIS. 



An accurate and profitable study of the chondriosomes and of Golgi's apparatus 

 in the testicle can not be made without an intimate knowledge of the whole process 

 of spermatogenesis, and especially of its last phase spermiogenesis. In this con- 

 nection von Korff's researches (1902) on the spermiogenesis of another marsupial 

 (Phalangista vulpina) proved to be of great help. The process in Phalangista 

 is so similar to that in Didelphys that it appears necessary to give a summary of 

 von Korff's paper. 



Since the work of Meves on the spermiogenesis of the guinea-pig, this phase 

 in the evolution of the seminal cells has been usually divided into four periods: 

 The first period extends to the formation of the so-called "Schwanzmanschette," 

 which, following Oliver's example (1913), I shall call the caudal tube; the second 

 ends with the disappearance of the same formation; the third extends to the time 

 of the expulsion of the spermatozoa into the lumen of the seminiferous tubules and 

 of the elimination of the major part of the cytoplasm; the fourth period includes 

 such changes as may take place subsequently changes which, in many cases, are 

 of minor importance. In Phalangista von Korff found that, as the caudal tube 

 appears and disappears suddenly, it is better to use as a basis for the subdivision of 

 spermiogenesis the modifications of the centrioles which coincide with the appari- 

 tion and disparition of the caudal tube; i. e., their close relationship with the 

 nucleus at the end of the first period and the beginning migration of the centriolar 

 ring which marks the end of the second period. It appeared also expedient to sub- 

 divide the second period according to the modifications of the nucleus: First, the 

 spherical nucleus is transformed into an egg-shaped body whose long axis is per- 

 pendicular to the axial filament; later it assumes its definite shape. 



The young spermatid of Phalangista contains two granular centrioles, located 

 first at the periphery of the cell, later moving toward one pole of the nucleus, while 

 the idiozome moves toward the other pole. The distal centriole carries a thin 

 filament and flattens out somewhat at the end of the first period. The modifica- 

 tions of the idiozome are less complicated in Phalangista than in other mammals. 

 Instead of the numerous granules, each located in a vacuole as noted in other 

 species (the guinea-pig for instance), a single vacuole without a granule is formed. 

 This attains a considerable size and applies itself to the nucleus, while the remainder 

 of the idiozome is eliminated. Von Korff mentions also a chromatoid body which 

 later falls to pieces and is probably cast off at the end of the process. 



The beginning of the second period is marked by the sudden appearance of the 

 caudal tube. The nucleus flattens out and later assumes its most characteristic 



