412 s. H ATTA : 



tlieni with the epibhist, &c.), the proiiephric system of Teleostei 

 and Amphibia shows, as stated in the liistorical review, the same 

 characters as that of Cyclostomata, so that the facts established 

 in Cyclostomata have the same significance for the Teleostei and 

 Amphibia. 



Although such is the case in those Craniota and Aiiiphio.uis, 

 the pronephros of Selacliia is quite otherwise : the Anlagen of 

 the pronephros are here formed in tlie mesoblastic somites posterior 

 to the Anlage of the liver (see below), and only one or two 

 segments of them are converted into the segmental duct (Rïjckert). 

 These pronephvic Anlagen in Selachia are, therefore, the mor- 

 phological equivalent, not of the glandular portion of the pronepliros, 

 but of those whieh are converted into the segmental duet in the 

 Craniota just mentioned. 



0. — The Segmental Duct in Selacliia is not the Blorphologieal 



Equirale)it of the Dud of the Same Name in C>/clostomafa, 



Teleostei, and Amphibia. 



Contradictory views arc met with in the derivation of the 

 segmental duct. The results arrived at in Cyclostomota, Teleostei, 

 and Amphibia, well agree in making it of the mesoblastic origin ; 

 there are a few authors who Ijelieve in the epiblastic origin of the 

 duct in these groups, but their papers are not more than mere 

 notes. In Selachia, the circumstance is reversed ; I am not aware 

 of any recent author other than Kabl, who advocates the meso- 

 blastic origin of the Selachian segmental duct. The facts given by 

 Rabl are, however, not the same as those observed in the 

 groups just referred to. In these, as stated above, the duct is 



