454 JOHN BEARD, 



And, finally in the 31 days foetus, while it showed concentric 

 corpuscles in one lobe of the thymus (Figs. 58 and 59), the rest of 

 the organ contained none. 



It was, therefore, resolved to carry no further a useless quest, 

 which, notwithstanding the assertions of Stieda ('81) as to the con- 

 centric corpuscles, could lead to no useful results, and would be but 

 waste of time. After all the labour on the thymus of the skate, on 

 the concentric corpuscles of the cavy, after all the results of the re- 

 searches of KÖLLIKER, Prenant, Schultze, Maurer, the writer, and 

 others, further attempts to refute a statement, which, as will be shown 

 anon, never had a better basis than an hypothetical one, seem uncalled 

 for. What may be demanded, however, is the production by Stieda 

 of some evidence beyond mere assertion of the accuracy of his con- 

 clusion of 1881. If there be anything in his hypotheses — and no- 

 thing is more certain than their baseless character — with the in- 

 formation as to the cavy contained in the present writing, it ought 

 not to be difficult for Stieda, or for one who maintains his thesis, to 

 produce a tardy, but necessary, proof of the same. 



As the 22 days embryo throws no light whatever upon the con- 

 centric corpuscles, it need no further concern us. Sections of the thymus 

 of each of the remaining foetuses were stained in two ways, with 

 picrocarmine, and with haematoxylin and eosin. The latter was the 

 more useful, for eosin stains the concentric corpuscles of either a 

 brilliant red, or partly red, partly purple. In the 31 days foetus, as 

 already stated, there were not concentric corpuscles in all the lobes. 

 In some of them no traces whatever of epithelial cells could be 

 made out. In others there are epithelial cells near the centre of the 

 lobe, forming a branching network. In what appears to be the main 

 lobe there are concentric corpuscles of small diameter, i. e., one only 

 in section, and of about 0.06 mm. Here, and in later cases also, though 

 it may become branched, and thus lose its primitive simplicity, the 

 concentric corpuscle has the form of a column of cells, arranged in 

 concentric fashion. In certain of them there is an obvious concentric 

 arrangement of epithelial cells, many or all of which are in degener- 

 ation, and exhibit chromatolysis. This latter is very clear in the picro- 

 carmine preparations. In this foetus of 31 days they do not stain of 

 so deep a red as in the later ones, and there is no marked epithelial 

 branching from the corpuscles. As to the rest of the thymus, it is 

 made up of leucocytes, and blood-vessels penetrate it everywhere. Here 

 and there, as in Fig. 58, there is a leucocyte in the concentric corpuscle. 



