82 



ESSAY ON CLASSIFICATION. 



Part I. 



The disagreement of authors as to the limits and respective value of its orders and 

 families may be partly owing to the unnatural circumscription of the class itself.^ 

 As to the Reptiles, it is already certain, that the Amphibia and Eeptiles proper, so 

 long united as one class, constitute two distinct classes. In the main, the develop- 

 ment of the true Reptiles^ agrees very closely with that of the Birds, while the 

 Amphibians'^ resemble more the true fishes. In no class are renewed embryological 



1856, vol. 17, p. 443.— MuLLER, (A.,) Ueber die 

 Entwickelung iler Neunaugen, Mulk-r's Arch., 185G, 

 p. 303. The unexpected facts mentioned here, render 

 it higlily probable, that Amphioxus is the immature 

 state of some marine Cyclostom. 



^ The peculiarities of the development of the 

 Plagiostoms consist not so much in the few large 

 eggs they produce, and the more intimate connection 

 which the embryo of some of them assumes with the 

 parent, than in the development itself, which, not- 

 withstanding the absence of an amnios and an allan- 

 tois, resembles clcsely, in its early stages, that of the 

 Reptiles proper and of the Birds, especially in the 

 formation of the vascular system, the presence of a 

 sinus terminalis, etc. Again, besides the more ob- 

 vious anatomical differences existing between the 

 Plagiostoms and the bony Fishes, it should be remem- 

 bered that, as in the higher Vcrtebrata, the ovary is 

 separated from the oviducts in the Sharks and Skates, 

 and the eggs are taken up by a wide fallopian tube. 

 That the Plagiostoms can hardly be considered sim- 

 ply as an order in the class of Fishes, could already 

 be inferred from the fact, that they do not constitute 

 a natural series with the other Fishes. I would, 

 therefore, propose the name of Selacpiians for a 

 distinct class embracing the Sharks, Skates, and 

 Chimajras. Recent investigations upon the Cyclos- 

 toms, show them also to differ widely from the 

 Fishes proper, and they too ought to be separated as 

 a distinct class, for which the name of jNItzontes 

 may be most appropriate. 



^ VOLKMANN, (G. W.,) De Colubri Natricis 

 Generatione, Lipsioe, 1834, 4to. — Ratiike, (H.,) 

 Entwickelungsgeschichte der Natter, (Coluber Na- 

 trix,) Konigsberg, 1839, 4to. fig. — Weinland, (D.,) 

 Ueber den Eizahn der Ringelnatter, Wurt. Nat. 

 Hist. Jahreshefte, 1855. — Tiedemann, (F.,) Ueber 



das Ei und den Foetus der Schildkriite, Heidelberg, 

 1828, 4to. fig. — Baer, (K. E. v.,) Beitriige zur 

 Entwickelungsgeschichte der Schildkroten, Miiller's 

 Archiv, 1834, p. 544. — Rathke, (H.,) Ueber die 

 Entwickelung der Schildkroten, Braunschweig, 1848, 

 4to. fig. 



' RosEL v. ROSENHOF, (A. .J.,) Ilistoria natu- 

 ralis Ranarum nostratium, etc., Norimb., 1758, fol. 

 fig. — Funk, (A. F.,) De Salamandra; terrestris vha, 

 evolutione, formatione, etc., Berlin, 182G, fol. flg. — 

 Rathke, (H.,) Diss, de Salamandrarum corporibus 

 adiposis eorumque evolutione, Berol, 1818. — Ueber 

 die Entstehung und Entwickelung der Geschlechts- 

 theile bei den Urodelen, N. Schr., Dantz. Naturf. Ges., 

 1820. — Steinheim, (L.,) Die Entwickelung der 

 Frosche, Hamburg, 1820, 8vo. fig. — Hasselt, (J. 

 CoNR., van.) Dissert, exhibens Observationes de 

 metamorphosi quarumdam partium Rana; temporaris, 

 GottingiB, 1820, 8vo. — Prevost, (J. L.,) et Lebert, 

 Memoire sur la formation des organes de la circula- 

 tion et du Sang dans les Batraciens, Ann. Sc. Nat., 3e 

 ser. I. p. 193, fig. — RuscONi, (M.,) Developpement 

 de la Grenouille commune, depuis le moment de sa 

 naissance jusqu' a son etat parfait, Milan, 1828, 4to. 

 fig. — Amours des Salamandres aquatiques et deve- 

 loppement du Tetard de ces Salamandres, etc., Milan, 

 1822, 4to. fig. — Baer, (K. E. v.,) Die Metamor- 

 phose des Eies der Batrachier vor der Erscheinung 

 des Embryo, etc., Miiller's Archiv, 1834, p. 481. 

 — Entwickelungsgeschichte, etc., vol. 2d, p. 280. — 

 Reichert, (K. B.,) Das Entwickelungsleben im Wir- 

 belthierreich, Berlin, 1840, 4to. fig. — Vergleichende 

 Entwickelungsgeschichte des Kopfes der nackten 

 Amphibien, etc., Konigsberg, 1838, 4to. fig. — Ueber 

 den Furchungsprocess der Batrachier-Eier, Miiller's 

 Archiv, 1841, p. 523. — Vogt, (C.,) Untersuchungen 

 iiber die Entwickelungsgeschichte der Geburtshelfer- 



