58 DE. W. G. EIDEWOOD OS THE 



true vertebrae ; that of von Ibering (9. p. 235), that the condition 

 is due to the secondary segmentation of vertebrae originally- 

 simple; that of Schmidt (15. p. 755), that two consegmental 

 vertebrae occurred primitively throughout the body, and now 

 persist only in the caudal region ; or that of Baur (2. p. 942), 

 and Hay (8. p. 5), that the pleurocentrum and hypocentrum 

 together constitute a single vertebra equivalent to those of the 

 trunk region, where the fusion of pleurocentra and hypocentra 

 is assumed to have occurred, — the same general conclusion 

 will apply as that above specified for Selachians, namely, that 

 the universal tendency to develop single vertebral bodies is, in the 

 region between the anus and the caudal fin, over-ruled by the 

 demand for increased flexibility. Indeed, the conclusion might 

 even be further extended to the Stegocephali, in which the 

 embolomerous type of vertebra prevails in the caudal region 

 only. 



List of Eefeeences. 



1. Balfoue, p. M. — Comparative Embryology. Yol. ii. 



London, 1881. 



2. Baue, G-.— "On the Morphology of Ribs." Amer. Nat. 



vol. xxi., Philadelphia, 1887 ; pp. 942-945. 



3. Feanqtje, H. — Nonnulla ad Amiam calvam accuratius co- 



gnoscendam. Berlin, 1847 ; pp. 14, one plate. 



4. GrADOw, H., and Abbott, E. C. — " On the Evolution of the 



Vertebral Column of Fishes." Phil. Trans. Eoy. Soc, 

 vol. 186. 1895, B (1896); pp. 163-221, numerous figures 

 in the text. 



5. Gegenbaue, C. — " Ueber die Entwickelung der "Wirbelsaule 



des Lepidosteus, mit vergl.-anat. Bemerkungen." Jena- 

 ische Zeitschrift, vol. iii., Leipzig, 1867 ; pp. 359-420, 

 three plates. 



6. GrOTTE, A. — Die Entwickelungsgeschichte der TJnke. Leipzig, 



1875. 



7. Hasse, C. — Das natiirliche System der Elasmobranchier 



auf Grrundlage d. Baues u. d. Entw. ihrer Wirbelsaule. 

 Jena, 1879. 



8. Hat, O. P. — " On the Structure and Development of the 



Vertebral Column of Amia." Field Columbian Museum 

 Publications, Zool. Series, vol. i., no. 1. Chicago, 1895 ; 

 pp. 54, 3 plates. 



