60 



cells may give rise to concentric capsules of epithelial cells, but only 

 in their atrophy and death. The conversion of a germ -cell into an 

 ordinary epithelial cell of the embryo would be a miracle without 

 parallel. But, of course, it should not be forgotten, that according 

 to current opinion germ-cells may, and do, arise from epithelial cells, 

 and, therefore, that what a germ-cell has been that it may again be- 

 come. But as little as the basis of fact for the first statement can 

 be allowed, so little can the logical necessity, or even the possibility, 

 of the second be admitted. Were there a particle of truth in either, 

 the reversion of Man to his childhood might well be within the range 

 of possibilities. 



Rabl's ^) depreciatory remarks concerning "versprengte Keime", 

 and the importance pathologists attach to such, were the main reasons 

 for the inclusion of Pristiurus within the scope of the research. Re- 

 cognising that, like earlier investigators, he had probably not adopted 

 suitable methods for the treatment of his embryos, the writer was 

 curious to see for himself the actual conditions in Pristiurus. And 

 now from the study of a small but sufficient number of embryos new 

 light has been thrown upon Rabl's rule. This it not very clearly de- 

 fined by him. And has he not himself recorded the occurrence of 

 germ -cells in various places, other than the "sexual gland", or its 

 future site? 



From my studies of the germ-cells the following rules have come 

 to be recognised, 1) that the original number is always a definite one 

 — 2n; or, subtracting that which goes to form the embryo. 2n — 1, and 

 that only a percentage of them find their way to the normal position, 

 the site of the future germinal nidus. As to the rest, it is, Rabl 

 notwithstanding, the rule, that for long periods of the 

 development they occupy one or other of many abnor- 

 mal positions, and that many of them degenerate here. 



When it is urged, that we possess no reliable knowledge of the 

 further fate of any such vagrant germ -cells, one need only refer to 

 the researches of Wilms ^), which appeared prior to the publication 



1) Like Balfour 25 years ago, Rabl is unable to account for the 

 particles (Körnchen) in the germ - cells of certain periods , and fails to 

 recognise their nature as yolk-plates. One can hardly take this failure 

 seriously. The marvel is, that with all the resources of a modern micro- 

 scopical technique by following back these structures in them, and in 

 earlier embryos in the somatic cells, to the cleavage he was unable to 

 elucidate their true characters. 



2) Max Wilms, Ueber die Dermoidcysten und Teratome etc. 

 Deutsches Arch. f. klin. Med., Bd. 55, 1895, p. 1 — 108, 3 Tab. And 



