676 JOHN BEARD, ' 



pluripolar mitoses, it may be permitted to indicate its consequences. 

 In an extensive, as yet unpublished, work on the thymus the thing 

 has also attracted attention in connection with Hassall's corpuscles, 

 but not in Raja. 



Pluripolar mitoses most generally, if not universally, soon reach 

 a limit. The cell-nests in epithelioma, cancer etc. all bear this 

 character. Whilst in ordinary mitosis the products are pressed apart, 

 and, finally, as a rule, separated, in the pluripolar form they tend to 

 remain aggregated, and to get closer and closer together. Moreover, 

 and this is the crucial point, they incline to a concentric arrange- 

 ment. Whilst ordinary mitosis might be termed centrifugal: pluri- 

 polar mitosis is centripetal. The former character otïers no limits: 

 the latter imposes very serious ones. Under its sway the area for 

 subsequent action is always becoming more and more restricted, and 

 very soon it is used up entirely. 



So much discussion would not have been devoted to pluripolar 

 mitosis, but for its evident prevalence, in what Rügkert has termed 

 "megaspheres". These I identify either as germ-cells, or, if they be 

 very large, as the fore-runners of such cells. Certainly, no such 

 actual pluripolar mitotic figures have been made out, but their results 

 are only too apparent. 



It is, therefore, concluded, that superfluous germ-cells may de- 

 generate in one of two ways. The first is a form of simple atrophy, 

 and the second is, perhaps, also atrophy, associated with pluripolar 

 mitosis and the formation of cell-nests. These nests may be either 

 within the yolk, or they may emancipate themselves from it. Moreover, 

 there is a strong temptation to regard this second form of degeneration 

 as primarily due to the initiation of pluripolar division. 



In certain of my embryos the second form seems to have many 

 representatives. It is to be hoped, that the reader will not measure 

 the amount of evidence for it by the number of figures in the plates. 

 The latter were drawn some time back, and long after this there was 

 hesitation in my mind about publishing them. Their nature has been 

 doubted and tested. Finally, after long consideration, and — what 

 is more — after renewed and careful study of the preparations and 

 of others as well, all doubt has disappeared. Along with other 

 characters their yolk and the duplication of the nuclei seem to me 

 decisive. They are not degenerating leucocytes, for among the count- 

 less thousands of the latter, examined or drawn under the highest 

 powers, not one has ever exhibited either of the above characters; in 



