56 CYTOPLASMIC STRUCTURES IN THE SEMINAL EPITHELIUM OF THE OPOSSUM. 



located at the periphery of the cell and perpendicular to its surface, with a thin 

 filament in connection with the distal centriole. 1 No chromatoid body was observed. 

 A number of fat droplets are invariably found in one heap quite near the periphery 

 of the spermatid; these very soon disappear (fig. 8). Their constant location at the 

 periphery, as well as a special lighter aspect of the protoplasm in that region, sug- 

 gests the possibility of an elimination in bulk. This process was not observed, 

 however, and consequently one may just as well admit that they are simply digested. 

 After a short period of growth the nucleus gradually diminishes in size while the 

 condensation of the chromatin is taking place. There is no change in the form of 

 the nucleus, but there is a change in its location. At the end of the first period it 

 has moved to the periphery of the cell opposite the centrioles (fig. 9) . 



The idiozome is composed of the same constituent parts as described for the 

 spermatocytes. Then, as in Phalangista (von Korff) a single vacuole appears 

 within the medullar part (fig. 8) ; this increases to rather considerable dimensions, 

 and coming in contact with the nucleus apparently exerts some pressure upon the 

 nuclear membrane, as the latter shows a marked degree of flattening (figs. A, 8 and 

 17). The nucleus, however, resumes its spherical shape as the zone of contact with 

 the vacuole becomes larger. Meanwhile, the cortical part of the idiozome has been 

 detached; we find it at the end of the first period loose in the protoplasmic lobe. 

 The head cap now extends over the anterior third of the nucleus, or thereabouts, 

 and a small granule, a sort of acrosome, can be seen, although no trace of it was 

 visible in the earlier stages (fig. 9). The centrioles, whose position, from the very 

 beginning of the process, determines what it is customary to call the posterior 

 pole of the spermatid, migrate toward the nucleus, and consequently the 

 axial filament increases in length. The proximal 

 centriole comes in close contact with the nuclear ^\ Fl : A - s P er . matid . in 



f/^ -Ov the first period, /eiss 



membrane and thus is often very difficult to detect. / ( V\ apochr.imm.2mm.,oc. 



. _ . .. . 11 \ , %/ * I \ 12. Fixation and stain: 



The distal centriole exhibits then a small excre- V Benda - The 



scence of granular form but somewhat elongated 

 in the direction of the mother-centriole (fig. A). 



In order to make the description more precise, I might add that under the 

 spermatids going through the process noted above one finds two discontinuous 

 layers; one of spermatogonia, the other of first spermatocytes. The latter exhibit 

 all stages of the first phase of the growth period and the beginning of the second. 

 Above is a layer of spermatids in all stages from the end of the second period (fig. 

 12) to the elimination of the spermatozoa. 



SECOND PERIOD. 



Here, as in Phalangista, the modifications of the nucleus would allow a sub- 

 division of this period. First, there is a gradual condensation of the chromatin, 

 until all structure disappears; at the same time the nucleus flattens out and assumes 

 the shape of an egg whose long axis is perpendicular to the axial filament (figs, c, 

 10, and 33) . Then other complicated changes occur which finally bring about a 



'This filament is seen beating actively in the living cell. 



