The origin and histogenesis of the thymus in ßaja batis, 457 



In his extensive researches upon the thymus, which unfortunately 

 are far more concerned with its minute structure than with its devel- 

 opment, Watney 1) writes : "In considering the function of the con- 

 centric corpuscles and their behaviour during involution, one point 

 must be apparent to all, i. e., that many of them disappear". He adds, 

 that there are few of them in the thymus of old animals, and that as 

 a rule these are small. 



Their disappearance is not remarkable, when their extreme de- 

 generation in even a new-born cavy is considered. 



As from the start they exhibit degenerative phenomena, and as 

 in such animals as the skate the thymus manages to get along and 

 function without them, their embryological importance is not, or at 

 any rate ought not to be, great. In the past too much value has 

 been attached to the existence of Hassall's corpuscles, with the 

 result that far weightier things have been neglected or misunderstood. 



Indeed, it may be doubted whether mankind would be much the 

 wiser, were a full and true history of the developmental origin of 

 Hassall's corpuscles extant. 



From the apparent absence of concentric corpuscles in fishes, 

 and from the description and figures of the epithelial bodies (Epithel- 

 körperchen of Maurer and Kohn) of Lacerta, as given by Maurer, 

 the origin of the concentric corpuscles from these as products of de- 

 generation does not appear unlikely. It had been hoped, that the 

 observations upon the cavy would have either confirmed or disproved 

 this. As the research into the cavy has not been completed, the 

 suggestion may be commended to the attention of future observers ^j. 



Xn. Historical. 



For a general survey of the results recorded in preceding pages 

 the reader may be referred to two recent publications ^). To sum- 



1) Herbert Watney, The minute anatomy of the Thymus, in: 

 Phil. Trans. Roy. Soc. London, V. 173, p. 1063—1123, tab. 83—95, 

 1882; 1. c. p. 1090. 



2) While the present writing was passing througli the press, Nus- 

 BAUM & Maciiowski and Prymak published further researches upon 

 the thymus and concentric corpuscles of Teleostei and Amphibians (vide 

 list of literature). I regret to have no space for an account of their 

 observations. Nor would it be desirable to consider their statements 

 as to the concentric corpuscles of Salamandra until the appearance of 

 the complete work. Prymak confirms Maurer's finds of concentric 

 corpuscles in Teleostei. 



3j Beard, J., A thymus-element of the spiracle in Kaja, in: Anat. 



