452 JOHN BEARD, 



XI. Hassall's Concentric Corpuscles of the Thymus 

 of the Cayy. 



The concentric corpuscles, so characteristic of the mammalian 

 thymus of certain periods, do not occur — apparently at any time — 

 in the skate. Or, to put the same thing in another way, neither in 

 embryos, nor in young, nor in adult skate has a single concentric cor- 

 puscle ever been seen by me in the thymus. Maurer (1885, p. 170) is 

 the only author i), who has recorded them as existing in fishes (Teleosts). 

 As already elsewhere stated, the single figure given — of three con- 

 centrically arranged cells, which may be leucocytes — does not con- 

 vince one, that the author really had a concentric corpuscle before 

 him. Certainly, if the structure were actually such a corpuscle, in this 

 instance they bear little resemblance to the bodies so-called in the 

 mammalian thymus. 



For the sake of completeness, and not because they are essential 

 constituents of the thymus, their absence in the skate, indeed, negativ- 

 ing this, it was resolved to work out their origin somewhere or other 

 in the mammals. Several forms were tried. Of these in the rabbit 

 there are no traces of concentric corpuscles as late as the birth-period, 

 when apparently the whole thymus is made up of leucocytes! They 

 are also absent in pig-embryos later than the oldest figured by Keibel. 

 Kittens and well-preserved human embryos were not at my disposal. 

 But an excellent object was found in the cavy. 



In new-born cavies, and even, as will be seen, at earlier periods, 

 the concentric corpuscles are so large, that in sections stained with 

 eosiu they can be seen with the unaided eye. Not only are they here 

 very large, far larger than in any mammal, in which they have yet 

 been described, but in appearance they are very remarkable, and quite 

 unlike any of those things, to which the term concentric corpuscle has 

 yet been applied. If they recall anything, it is the cell-nests of epi- 

 thelioma. In most courses of histology it is, I believe, the custom to 

 demonstrate the concentric corpuscles on preparations from young 

 children or kittens. As a remarkable contrast to such preparations, 

 sections of the thymus of a young cavy, say of a week or ten days 

 previous to the birth-period, or failing such of new born cavies them- 

 selves, may be recommended as worthy of attention. 



On finding such an excellent object in the cavy for the study of 

 the development of the concentric corpuscles, it was for the writer a 



1) Compare note page 457. 



