294 BULLETIN OF THE 



general results of these two investigators have been confirmed by Bonnet 

 ('87 and '88) in the Dog and Sheep, and a number of former advocates 

 of a mesodermal origin have satisfied themselves of the correctness of the 

 opposed view by a study of the preparations of these authors ; e. g. His 

 (see Spee, '84, p. 93),Waldeyer (see Janosik, '85, p. 13), and Mihalkovics 

 (see van Wijhe, '89, p. 501). 



The most recent paper on this subject is that of H. Meyer ('90), who 

 claims an ectodermal origin for the Wolffian duct in man. The embryo 

 upon which these observations were made was obtained by artificial 

 abortion, and was at once preserved by histological methods ; so that, 

 in the opinion of the author, it would be unfair to ascribe his results to 

 imperfect preservation, which so frequently renders observations on 

 human material untrustworthy. On the other hand, the mode in which 

 t'he duct is here claimed to originate, viz. as a conspicuous fold of ecto- 

 derm, is so different from the method of origin described in oilier Mam- 

 mals that one cannot regard this observation based on a single specimen 

 as conclusive evidence. 1 



A few recent writers have reasserted the mesodermal origin of the 

 Wolffian duct even in the case of Mammals. Lockwood ('87, p. 642) crit- 

 icises the evidence adduced by Graf Spee and Flemming, and compares 

 their ectodermal ridge to a number of insignificant ectodermal thicken- 

 ings which may be observed over depressions in the underlying tissue in 

 diverse regions of the body. Lockwood entirely ignores the very defi- 

 nite relations which Graf Spee showed to exist at a certain stage between 

 the fundament of the duct present in anterior regions and the continuous 

 posterior ridge ; his entire criticism therefore seems to me quite unwar- 

 ranted. Fleischmann ('87) also reasserts in a preliminary note the meso- 

 dermal origin of the duct in Carnivora ; but his description of the mode 

 of origin is so entirely at variance with the accounts of recent authorities 

 that his statements can hardly be regarded satisfactory before the evidence 

 on which they are based is produced. 



On the other hand, Martin (Stahl und Martin, '86, Martin, '88) accepts 

 tie main features of the development as described by Graf Spee and 



1 During the correction of these proof-sheets another paper has appeared which 

 asserts a participation of the ectoderm in the formation of the duct in Man (Kollmann, 

 '91). In the region of the middle plate there is found, according to this author, a 

 close fold of ectoderm (Taf. III. Figs. 3, 4, Anlmje d. Urniere, Fig. 8 a ) which he 

 believes to he concerned in the formation of the duct, thus confirming Meyer's ('90) 

 account. The later stages studied by Kollmann, however, are too far advanced 

 to afford convincing evidence that his interpretation of the fate of this fold is 

 accurate. 



