292 BULLETIN OF THE 



It will therefore be of interest to review critically the most recent 

 accounts in the several groups, for the purpose of ascertaining whether 

 the ectodermal origin of the segmental duct be in any case actually 

 demonstrated. For this purpose, only those papers which have ap- 

 pealed since Graf Spee's researches need concern us. Of these, the 

 larger number are brief notices, which, in view of the extreme difficulty 

 of the investigation, cannot be regarded as conclusive. 



In regard to Gyclostomes, the only papers that have appeared during 

 this period have been preliminary notices ; that of Kuplfer ('88) main- 

 tains an ectodermal, those of Goette ('88) and (Jwsjannikow ('89) a 

 mesodermal, origin for the duct. 



In Teleosts, the duct has been claimed to be ectodermal by Brook 

 ('87) and Ryder ('87) ; but on the basis of my own observations, which 

 are as yet incomplete, I am led to doubt the correctness of this claim, 

 which has already been opposed by the observations of Henneguy ('88), 

 of H. V. Wilson ('90), and of Mcintosh and Prince ('88). In the 

 account by Brook, it seems to me probable that the ectodermal thick- 

 ening observed has in reality a very different significance (lateral line 

 proliferation) from that attributed to it, an opinion which is shared by 

 Wilson ('90, p. 58). The only recent paper dealing with the develop- 

 ment of the Ganoidean excretory system is the preliminary notice of Beard 

 ('89) on Lepidosteus. According to Beard, the duct is ectodermal. 



In Amphibia, also, an ectodermal origin of the segmental duct has 

 been asserted by Perenyi ('87) and by Brook ('87). Their communi- 

 cations, however, are both short notices, and in the absence of the final 

 papers cannot be regarded as satisfactory evidence. Moreover, the meso- 

 dermal origin of the duct has been reaffirmed by Mollier ('90), Kellogg 

 ('90), and Marshall and Bles ('90). 



It is rather remarkable, that, in all the preceding classes, nothing but 

 preliminary notices have ever appealed in favor of the ectodermal view. 

 The same is true of Birds, where this mode of origin has been claimed 

 as probable by Beard ('87) and by Brook ('87). On the other hand, 

 a number of observers have carefully investigated the chick with this 

 special purpose in view, aud have been unable to find any evidence of a 

 participation of the ectoderm in the formation of the Wolffian duct. 

 Among these may be mentioned JanoSik ('85), Mihalkovics ('85), and 

 Hoffmann ('89). Peculiarly significant, however, is the fact that Graf 

 Spec (!<('>) was unable with the use of the most various reagents to see 

 any direct evidence of a genetic connection between the ectoderm and 

 the Wolffian duct in the Chick. 



