THE YPSILOID APPARATUS OF URO DELES. 271 



extreme end. However, I have not succeeded in ^obtaining 

 either a Spclcrpcs or a Desmognathus of a stage just previous to 

 the formation of this connection between the two halves of the 

 pubis, and I am not sure, therefore, that the median unpaired 

 portion ever exists as a separate cartilage arising like the ypsiloid 

 cartilage anterior to the pelvic girdle and independent of it. If 

 it has such a separate origin it is undoubtedly a vestige of the 

 stem of the ypsiloid cartilage. 



C. Tlic Hoinology of the Ypsiloid Apparatus. 



There are two diametrically opposed views as to the homology 

 of the ypsiloid cartilage. One of these is that indicated by the 

 quotations given earlier in this paper, viz., that the Cartilago 

 ypsiloidcs is the homologue of the median anterior process of the 

 pubis (Processus epipnbicns] such as is found either single or 

 paired in certain of the Perennibranches and Derotremes. More- 

 over, this homology is extended to include the similarly situated 

 process in various Selachians, Ganoids and Dipnoans. This 

 opinion as to the homology of the ypsiloid cartilage has been 

 held very strongly by C. K. Hoffmann ('73-' 78) and R. Wieders- 

 heim ('92) and corroborated by certain observations of H. Riese 

 ('91). Aside from general similarity of location of the ypsiloid 

 cartilage and the Processes epipnbicns the homology is apparently 

 based upon a continuity of the cartilage tissue of the pubis with 

 that of the stem of the ypsiloid cartilage. This condition is, as 

 has been shown, not the usual one in the adult, although Riese 

 ('91) found it to exist in Tylototriton verntcosits, and Wieders- 

 heim has noted in the case of old individuals of other species a 

 condition which he designates as a secondary fusion. Wieders- 

 heim says, however, regarding the adult condition, that " Man 

 bei histologischer Untersuchung in Allgemeinen viel haufiger 

 auf verbindende Knorpelbriicken zwischen der Hauptmasse des 

 Beckens und dem Epipubis stosst, als man dies nach der ein- 

 fachen Preparation mit Messe und Pincette ervvarten sollte." 



In Triton alpestris larvae Wiedersheim found, as I have done, 

 that the ypsiloid cartilage arises by an independent anlage, but in 

 larvae of Triton Jielveticus and in a 26 mm. Axolotl he found 

 the cartilage element continuous, although he adds : " Diese 



