456 JOHN BEARD, 



cavy do not, unfortunately, clear up the mode of origin of these 

 structures. They fulfil the following purposes, to wit, they establish 

 for the cavy a period of the development, during which such con- 

 centric corpuscles are in formation ; and, if such a demonstration 

 were needed, they prove these corpuscles to be products of de- 

 generation. 



The question, whether they arise from remains of the original 

 epithelium, or from leucocytes, or from epithelial cells in process of 

 conversion into leucocytes, cannot be finally solved without new re- 

 search. At the moment the writer has neither the desire, nor the 

 time, to undertake this. The long columnar form of the concentric 

 corpuscles in the cavy is suggestive of their origin from the remains 

 of the original epithelial tube. On the other hand, the difficulty of 

 establishing the existence of remains of this tube in late periods, prior 

 to the appearance of concentric corpuscles, does not point in this 

 direction. In the rabbit near birth, and in the sheep of 35 mm, 

 according to Stieda's observations subsequently cited, and in some 

 of the lobes of the 31 days cavy, the whole thymus is lymphoid, and 

 little or no remains of epithelial cells can be made out. 



Two important features of the concentric corpuscles should be 

 especially noted: they are degenerative structures without doubt — 

 the chromatolysis in many of the component cells sufficiently evidenc- 

 ing this — and from their structure they are obviously products of 

 pluripolar mitosis. 



In the first part of my work on the "Germ-Cells", now in the 

 press ^), it has been shown, that germ-cells often degenerate with 

 pluripolar mitosis and the formation of cell-nests, comparable to con- 

 centric capsules. If degeneration of germ-cells be accompanied by 

 phenomena of this kind, there would, apparently, be no reason why 

 such should not possibly hold for leucocytes also. As in the germ- 

 cells, it is probable, that with the start of the formation of a con- 

 centric corpuscle pluripolar mitosis is connected. Whether the happen- 

 ing of this in an epithelial cell, or in one in process of conversion 

 into a leucocyte, or in a leucocyte itself, be the beginning of the pro- 

 cess seems to me immaterial. So much is now certain: from the 

 majority or all of the original epithelial cells leucocytes arise, and 

 the concentric corpuscles of Hassall, where found, are mere products 

 of degeneration. They can have no morphological import, and it is 

 open to grave doubt whether they even possess any physiological value. 



1) in: Zool. Jahrb., V. 16, Anat., p. 615—702, 1902. 



