CYTOPLASMIC STRUCTURES IN THE SEMINAL EPITHELIUM OF THE OPOSSUM. 57 



peculiar form of the nucleus, roughly comparable to that of a swallow's tail. The 

 process has been described by von Korff (pages 254-255) , and is further illustrated 

 to a certain extent by my figures, so that it is not necessary to dwell upon it. 



During the first phase of the nuclear modifications the rest of the idiozome is 

 still found as a single, solid body in the v /t \ FIGS. B and c. Twospcr- 



nrntrmlfl^rmV Inbp (fitr*t R r nrul 10 s ! l( ( ( f\ I niatids in the first phasr 



ngS. a, C, an A \ \Ljt O f the second period. 



Afterwards it disintegrates into particles ( 1 / / I / Zeiss a P chr - m -. ~ 



\ \ / \ / mm., oc. 12. Fixation 



formed of granules. These fragments, in V \/ V 1 / and stain: Benda. The 



, . . 1 , . IL-'-^Sl \ \ i chondriosomes have 



preparations which show the chondno- T^i l~~k\ imrp.,sfi y not been rep- 



somes, are usually more or less covered by ^^ ^ --' 



the latter bodies and are therefore difficult to detect. One of them, however, is 

 generally conspicuous on account of its location. It is found near the opening of 

 the caudal tube, sometimes even within it, and remains there throughout this 

 period (figs. 11 and 12). The headcap now covers the anterior half of the nucleus 

 (fig. B), and the acrosome, already referred to as appearing at the end of the first 

 period (fig. 9), has become quite conspicuous. With the gradual flattening out of 

 the nucleus the headcap becomes more and more closely attached to it and can be 

 recognized only when the nucleus has shrunken somewhat (in figure c the nucleus 

 exhibits a slight amount of shrinkage); otherwise only a slight thickening of the 

 anterior edge of the head is noticeable. Later, with the beginning of the second 

 phase of the nuclear modifications, a peculiar appearance is observed. From the 

 pointed extremity of the head emerges a process which projects as a sort of spur 

 into the Sertoli cell (fig. 11). 



In a still later stage (fig. 12) this structure has extended toward the other 

 extremity of the head; thus the anterior edge of the nucleus appears, so to speak, 

 duplicated. The two parts are connected at their extremities by an oblique line, 

 and between by two rather thick trails of a sharply stainable substance. This 

 condition is plainly visible after all fixations except mat of Regaud. Comparing 

 figures 11 and 12, one gets the impression that something has become disjointed 

 from the nucleus but still adheres to it by means of this stainable material. The 

 two trails persist for a long time in the protoplasm of the Sertoli cell, so that one 

 may infer that the structure has not been put back into its original position. What 

 becomes of it I could not ascertain. It seems probable, however, that here we have 

 to deal with the elimination of the headcap, a process which von Korff was able to 

 observe more clearly in Phalangista. The disappearance of the structure described 

 would then be due to its digestion by the Sertoli cell. 



We left the centrioles at the end of the first period as three granules : the proxi- 

 mal centriole, the distal centriole, and its process. While I feel justified in asserting 

 that the further modifications of these granules are very similar to those described 

 for other mammals, and belong to a type in many respects very close to those found 

 in Phalangista, yet the process could not be followed in any great detail. The lack 

 of good iron hematoxylin has already been mentioned. Three other factors also 

 intervene to make the study difficult: (1) The eventual presence within the caudal 

 tube (and in close proximity to the centrioles) of a fragment of the idiozome; (2) 



