607 



In the epididymis of the rat conditions are very similar to those 

 described lor mouse, except that no such large cuboidal cells appe- 

 ared in my sections, and to that extent left this tissue less favorable 

 ior detailed study. Not a single mitotic figure was seen; on the other 

 hand, amitoses of all stages were abundant. 



In the bull the columnar epithelium of the epididymis is compo- 

 sed of very tall cells, densely crowded, and with long narrow oval 

 nuclei. Mitoses are absent. Amitoses are abundant, the plane of 

 division being almost invariably in the long axis of the nucleus and cell. 



The epididymis of the horse resembles that of the bull, except 

 that the nuclei are less rod-like, i. e. more oval, like in the mouse and 

 rat. The cilia here also appear much longer, being from ^g to ^l^ the 

 length of the cell, are especially well preserved and clearly arise from 

 a row of granules on the distal margin of the cell Division figures 

 are rare, but both mitotic and amitotic examples are present. Ami- 

 toses preponderate, but apparently not greatly, and are limited to 

 the more basally located nuclei. All mitotic spindles and figures were 

 situated near the distal border. It does not appear that they belong 

 to young cells growing toward the lumen, i. e. basal cells changing 

 to columnar elements and without cilia, for masses of cilia are attached 

 to the cytoplasm of which they apparently are the nuclei. Nor are 

 they probably proliferating leucocytes among the cells, as might be 

 surmised, for they appear to be directly in the cell protoplasm, and 

 sometimes surrounded by a clear halo. This single exception of 

 mitoses in ciliated epithelium will be further discussed in the next 

 section. It must be noted also that in the horse the amitotic divisions 

 are largely limited to the smaller more chromatic, apparently less 

 virile, nuclei. 



In the epididymis of the young rabbit of 4 weeks, where mitoses 

 would be expected, not a single figure can be seen. Cilia have not 

 yet developed. The pseudo-stratified epithelium consists of short 

 columnar cells. Occasional amitoses appear, but in view of the ab- 

 sence of mitoses, they are unexpectedly rare. 



In the epididymes of the dog, opossum and mule, mitoses are 

 absent, and amitoses infrequent. 



In the trachea of the cat nuclear amitoses are frequent in the 

 ciliated cells, and mitoses apparently do not occur. 



In the ciliated cells of the gills of Unio, both mitoses and amitoses 

 occur, but only very rarely in either type. Here again it could not 



