610 



the direct method ; or, in certain instances of neoplastic growth, to 

 atypical mitoses. That the restraining influence may exert only a 

 temporary effect is clear from Nathansohn's well known experiments 

 with spirogyra where the presence of a few drops of ether in the water 

 determined amitosis (probabl}' by stupifing the centrosome), which 

 was again followed by normal mitosis on return to fresh water; and 

 also by the numerous observations that spermatogonia may divide 

 by amitosis, and their descendants, the spermatocytes, again by 

 mitosis. 



Summary and conclusion. In the epididymis of the white 

 mouse amitosis is the exclusive method of division oi the ciliated epi- 

 thelial cells. In the vasa efferentia, due mainly to the larger size of 

 the cuboidal cells, the complete process can be followed with absolute 

 precision. Approximately one in five nuclei are at some stage of 

 direct division. Every possible phase is available, including cyto- 

 plasmic division.^) There is no regularity with respect to the orien- 

 tation of the nucleus in the cells; no uniformity as to the plane of 

 division with respect to the shape or position of the nucleus; nor any 

 similarity in the staining reaction of the mother or daughter nuclei 

 at the several stages of amitosis in different cells. In the vas epidi- 

 dymis the relative number of amitoses is slightly reduced and the 

 cytoplasmic process is more difficult, or impossible, to trace. Not 

 a single mitotic figure appears in this tissue. Basal granules and 

 marginal plates are present throughout the epididymis. These 

 structures are also especially distinct in the epididymis of the horse. 



The conclusion is suggested, and further supported by observa- 

 tions on the epididymis of rat, horse, bull, mule, rabbit and dog, and 

 the trachea of the cat and the ciliated cells of the gill of Unio, that the 

 fundamental cause of amitotic cell division in ciliated cells is the 

 destruction of the centrosome in the formation of the basal bodies 

 from which the cilia develop. If true basal granules are actually 

 wanting in the case of the non-motile cilia of the epididymis proper, 

 and the centrosome remains intact as seems to be the case in man 

 according to Fuchs, then the explanation of amitosis in this location 



1) Absolutely certain instances of cytoplasmic succeeding nuclear direct 

 division are relatively very rare. However, the absence of typical bi-nucleate 

 cells, i. e., with two nuclei separated by any considerable space, leaves no 

 doubt that the complete process is consummated, and that complete amitotic 

 cell-division prevails. 



