647 _ 



that all epithelia or epithelial organs arise either from epiblast or hypo- 

 blast. Two years more passed before serious attention was directed 

 to the question: and, independently, Flemming in the rabbit, and 

 VAN VVijHE^) in Raja confirmed the above result. 



Quite recently Dr. J. v. Perenyi ^) briefly states a similar find 

 in Rana esculenta and Lacerta viridis. 



Still those embryologists who hold, more or less, the Annelidan 

 origin of Vertebrates refrained from claiming the discovery as so 

 much on their side, van Wijhe, who does not count himself as one 

 of these zoologists, at the same time as he records his discovery also 

 puts in a protest against its annexation by the above schools. 



My finds in two genera of Elasmobranchs, Scyllium and Torpedo, 

 I now describe for two reasons. 



The epiblastic origin of the pronephric duct is so important that 

 it is interesting to know in how many forms such an origin occurs, 

 and especially in how many of the lower Vertebrates. Secondly, such 

 an origin in Scyllium is worth recording because of Balfour's posi- 

 tive statements of its mesoblastic nature in that genus. 



The agreement in mode of development of the segmental duct 

 in Mammals and Selachians leads one to expect that its epiblastic 

 nature throughout the Amphibia will sooner or later be proved, 

 possibly after much dift'icult research. In the Newt I have been unable 

 to satisfy myself on this point, but I think I may safely say that 

 FüRBRiNGER^) had not seen its first origin in Amphibians, and that 

 the stages, in which he figured and described its development in 

 mesoblast, are later than that in which it is really first formed. 



Shortly before its formation it is difi'icult in many places to 

 distinguish the boundaries of epiblast and mesoblast in Amphibia. 

 If confirmed Perenyi's find in Rana esculenta is very satisfactory, 

 and almost allows us to assume such an origin throughout Amphibia. 



I have in my possession only two embryos which show the 

 origin of the segmental duct in Selachians ^). 



1) Flemming, Die ectoblastische Anlage des Urogeuitalsystems etc. 

 Archiv f. Anat. u. Physiol., 1886, p. 236. 



2) VAN Wijhe, Die Beteiliguug des Ectoderras an der Entwickeluug 

 des Vornierenganges. Zool. Anz., 1886, No. 236. 



3) Zool. Anzeiger, 1887, Jan. 3P^, No. 243, p. 66. 



4) FiJBBEiNGEit, Die Entwicklung der Amphibienniere. Morphol. 

 Jahrbuch, 1877. 



5) Even in the chick it is not impossible to find traces of an epi- 

 blastic origin. Before the duct is formed, i.e. in embryos with 9 or 10 



