ON THE HEAD KIDNEY OF BDELLOSTOMA. 179 



very little evidence. Balfour and Mitsukuri give no definite 

 account of the mode of origin of the cell mass, their observa- 

 tions beginning at a time when it is already formed. Braun 

 considers that in Reptiles it commences by the formation 

 of aggregations of cells round branches of the vena cava, 

 while admitting ^ that " the rudiment .... is often so close 

 to the segmental tubules at their point of exit from the Mal- 

 pighian capsules, that one is easily led to believe in the 

 existence of a connection between the two.'^ But the most 

 striking observations on this point are those of Janosik, who 

 finds that in Mammals there is, immediately in front of the 

 Miillerian duct — that is, in the position of the head kidney — a 

 number of solid cords of cells, connected at intervals with the 

 peritoneal epithelium, and resembling exactly, so far as one can 

 judge from the account given, a series of solid rudimentary 

 segmental tubules. These striugs of cells have no connection 

 with the renal duct, but pass directly into the cortical substance 

 of the suprarenals.3 



Such fragmentary observations as I have hitherto been able 

 to make lead me to hope that I may be able at no very distant 

 date to show that, at all events in Reptiles and Mammals, the 

 connection between the Wolfiian body and the suprarenal is 

 much more intimate than has generally been supposed. But 

 should this hope prove unfounded, and should subsequent 

 observations prove that the primitive mesoblastic rudiment 

 arises simply as a mass of cells lying dorsal to the Wolffian 

 body, this would by no means afford sufficient reason for assert- 

 ing that the one structure had never been connected with the 

 other, for we know that precisely the same kind of separation 

 of two primitively continuous parts of the kidney has taken 



' Loc. cit., p. 23. 



- A short time before the appearance of Dr. Janosik's paper, Dr. Rensou 

 published in the 'Archiv fiir Mikroskopische Anatomie' (Bd. 22, p. 600), an 

 account of some observations which tend to prove the presence, in earlier 

 mammalian embryos, of functional segmental tubules in the position of the 

 solid cords of Janosik. As neither of these authors figure tlie structures 

 described, it is impossible to judge how far the one set may prove ideutical 

 with the other. 



