48 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



One objection against this hypothesis may be urged in the case 

 of Lepisosteus and all the amphibians. In all of these the interver- 

 tebral ring becomes cross-segmented, and the parts are distributed 

 to different vertebrae, the anterior portion becoming the hinder end 

 of the vertebra in front, the hinder portion the front end of the ver- 

 tebra behind it. In answer to this objection it may be said that orig- 

 inally the intervertebral ring, whatever its origin, is an integral mass 

 of cartilage ; that is, after the fusion of the circle of constituent 

 pieces ; and that the transverse segmentation is also a secondary 

 matter. It certainly would not be difficult to find examples of this 

 secondary segmentation of cartilage in many animals. 



A further objection against homologizing the invertebral carti- 

 lages of the Urodeles with the intercalated cartilages of Amia, may 

 be found in the apparent fact that the intervertebral ring of the Uro- 

 deles is located between the inner and the outer sheaths of the noto- 

 chord. Hasse's observations (35) appear to prove that such is the 

 fact ; nevertheless, it is desirable that they shall be confirmed. Geg- 

 enbaur did not reach the same conclusion. Hasse, in the paper just 

 referred to, and elsewhere, regards the intercuticular position of the 

 cartilages as indicating a relationship between the Elasmobranchs 

 and the Dipnoi, on the one hand, and the Urodeles on the other. 

 Later (39, p. 91) he concludes that, as regards the Dipnoi, he is prob- 

 ably wrong, and that the just named group does not stand in close 

 relation with the Urodeles. The so-called elastica externa of Dipnoi 

 and the cartilaginous Ganoids may, after all, be the homologue of the 

 inner sheath of Elasmobranchs. 



In view of these difficulties and doubts it appears to be easier to 

 believe that the intercalated cartilages have, through pressure or some 

 other influence, caused the elastica to be dissolved, and have thus 

 come to lie in contact with the inner sheath. It is to be noted that 

 the groups of cells which, in the salamanders, give origin to the inter- 

 vertebral rings, are placed exactly where we should expect the inter- 

 calated cartilages to appear. In T-jito:* tceniatus, investigated by 

 Hasse, these appear in the intervals between the successive arches 

 above ; while on the lower side of the notochord, they form one cen- 

 ter in the middle line, as though from a coalescence of the two lateral 

 masses. 



Gegenbaur attached much importance to the existence of the 

 intervertebral cartilages in the vertebral column of the amphibians. 

 He says, "Allen aber ist mit Auftreten des Intervertebralknorpels 

 ein eigenthiimliches Unterscheidungsmoment gegen die Fische 

 hingeworden. und in dieser neuen Bildung is zugleich eine fur die 



