466 JOHN BEARD, 



ture as much true thymus as the dorsal ones, and they have nothing 

 in common with epithelial bodies. If they represent such, where are 

 the epithelial bodies in other fishes? Finally, it may be remarked, 

 that unsupported by investigation no value can be attached to Maurer's 

 opinion as against that, based upon actual research, of a histologist 



like SCHAFFER. 



In his book on embryology Oscar Schultze (1897, p. 378 — 381), 

 from independent researches upon the development and histogenesis 

 of the thymus in Vespertilio murinus, has also adopted Kölliker's 

 conclusions, and, again, the history of the concentric corpuscles was 

 not traced. Regarding the thymus, in brief words Schultze's con- 

 clusion is, that "das epitheliale Organ wandelt sich direct in ein so- 

 genanntes lymphoides Organ um". 



Maurer is of all observers the one, who has devoted longest time 

 to the study of the thymus, as well as to other organs in its neigh- 

 bourhood. His researches extend over many years, and include Tele- 

 ostei, Amphibia, Lacerta and Echidna. I have refrained from citation 

 of his earlier work upon the histogenesis of the Teleostean and 

 Amphibian thymus, for, while he in these gave correct accounts of its 

 origin, his statements as to its histogenesis, as he himself now re- 

 cognises, have not found confirmation in his later researches in Lacerta 

 and Echidna. In these researches, which date from 1899, Maurer's 

 conclusions as to the histogenesis of the thymus may be gathered 

 from the following: "Die epithelogenen Elemente der Thymusanlage 

 bilden das adenoide Gewebe der Thymus". In this way, and 20 years 

 later, Kölliker's statements receive a new confirmation from Maurer's 

 researches in Lacerta and Echidna. 



On this follows my work of 1900, in which a further step is taken. 

 This, which is also the main theme of the present writing, is to the 

 effect, that the thymus is not only a source of leucocytes, but, more- 

 over, that it is the first place of their origin in the development, and 

 as such probably the only original source. 



Immediately after the publication of this there appeared the latest 

 paper upon the histogenesis of the thymus. This is by Josef Nus- 

 BAUM & Theodor Prymak (1901). The material used was Teleostei, 

 chiefly trout. The results of this research also go to prove the con- 

 version of the original epithelial cells into leucocytes. 



And now, to sum up the results of researches into the histogenesis 

 of the thymus. As we have seen, in 1880 His suggested, that the 

 leucocytes of the thymus had wandered into this organ, in this way 



