274 BULLETIN OF THE 



ment, apparently unknown to Hoffmann, that the duct first appears in 

 short fragments, each of which lies posterior to a segmental vesicle, 

 could be readily brought into accord with these observations. 



In regard to the correctness of Hoffmann's conclusions that these evagi- 

 nations represent a pronephros, I am of opinion that there is considerable 

 room for doubt. The organ described by Hoffmann differs in two im- 

 portant respects from that of Selachii, and from the young stages of the 

 Amphibian pronephros as presented in the first part of this paper. In 

 the latter groups, while the metameric evaginations are yet continuous 

 with the coelom, they have also fused distally to form a longitudinal 

 canal (collecting trunk) ; this condition I wholly miss in Hoffmann's 

 account, according to which all the evaginations remain distinct from 

 each other till they have entirely separated from the coelom, and only 

 the more posterior outgrowths ever fuse together. Secondly, no struc- 

 ture comparable to the Amphibian glomus is described. The latter 

 objection would apply equally to the account given by Mihalkovics. 1 

 None of the previous investigators were more successful in finding 

 glomeruli of the pronephric type. 



In regard to the former feature, however, the account of Mihalkovics 

 is more satisfactory, since the most anterior three pairs of vesicles stand 

 in precisely this relation to the body cavity and to the collecting trunk 

 (segmental duct). In reviewing Mihalkovics's interpretation, Hoffmann 

 says ('89, p. 272), since " die Vorniere als eine Ausstiilpung, die Urniere 

 nicht als solche entsteht, kommt es mir hochst wahrscheinlich vor ; dass 

 die Vermuthung von Mihalkovics, nach welcher die proximalen Urnieren- 

 kanklchen der Eidechsen der Vorniere der Amphibien entsprechen, eine 

 andere Deutung zulasse." I judge from this passage that Hoffmann is 

 inclined to regard as mesonephric tubules the anterior three or four seg- 

 mental vesicles described by Mihalkovics. I am quite unable to har- 

 monize this view with Hoffmann's prior identification ('89, pp. 267, 2G8) 

 of the pronephric evaginations described by him with the segmental 

 vesicles of Mihalkovics and Weldon. The mode in which the meso- 

 nephric tubules develop in Lacerta is asserted to be very similar to that 

 described by Riickert and van "Wijhe for Selachii. If I properly under- 

 stand Hoffmann's description, the space lettered c. in Tafel XVII. Figs. 3 

 and 4, is the lumen of a mesonephric tubule. From these figures it is 

 evident that the mesonephric tubule develops from a portion of meso- 

 derm ventral to the pronephros ; but according to both Riickert and van 



1 Figures 18 and 19, referred to by Wiedersheim ('90 b , p. 413) in this connection, 

 do not relate to Reptiles at all. They represent sections of Duck embryos. 



