METAMORPHOSES OF ANIMALS. 



123 



division, since the development of the Plagiostoms differs 

 greatly from that of the ordinary fishes. As it now stands 

 in our systems, the class of Fishes is certainly the most 

 heterogeneous amonQ- Vertebrata. The disagreement of 



O O 



authors, as to the limits and respective value of its orders 

 and families, may be partly owing to the unnatural cir- 

 cumscription of the class itself. l As to the Reptiles, it is 



family, Amer. Journ. Sc. and A., 1853, 

 vol. 16, p. 380. Embryology of Lo- 

 phiusAmericanus i PiOG.Aro..A.c.l855. 



LEREBOULLET, (A.,) Recherches sur 

 1' Anatomic des organes genitaux des 

 animaux Vertebres, N. Act. Ac. Nat. 

 Cur., vol. 23, p. 1. Resume d'un 

 travail d'embryologie compares sur 

 le developperueut du Brocket, de la 

 Perche et de 1'Ecrevisse, Ann. Sc. 

 Nat., 4e ser., 1854, vol. 1. AUBERT, 

 (H.,) Beitrage zur Entwickeluugs- 

 geschichte der Fische, Zeitsch. f. wiss. 

 Zool., 1853, vol. 5, p. 94 ; 1855, vol. 

 7. VALENTIN, (G-.,) Zur Entwickel- 

 ungsgeschichte der Fische, Zeitsch. 

 f. wiss. Zool., 1850, vol. 2, p. 267. 

 LETTCKART, (R.,) Ueber die allmahlige 

 Bildung der Korpergestalt bei den 

 Rochen, Zeitsch. f. wiss. Zool., 1850, 

 vol. 2, p. 258. HAECKEL, (E.,) Ueber 

 die Eier der Scomberesoces, Miiller's 

 Arch., 1855, p. 23. RETZITJS, (A.,) 

 Ueber den grosseu Fetttropfen in den 

 Eiern der Fische, Miiller's Arch., 

 1855, p. 34. BHUCH, (C.,) Ueber die 

 Micropyle der Fische, Zeitsch. f. wiss. 

 Zool., 1855, vol.7, p. 172. REICHERT, 

 (K.B.,) Ueber die Micropyle der Fisch- 

 eier, etc., Miiller's Arch., 1856, p. 83. 

 Ueber die Miiller-Wolffschen Kor- 

 per bei Fischembryonen, etc., Miiller's 

 Arch., 1856, p. 125. DerNahrungs- 

 dotter des Hechteies eine contractile 

 Substanz, Muller's Arch., 1857, p. 46. 

 DOWLER, (B.,) Discovery of a Vivi- 

 parous Fish in Louisiana, Amer. Jour. 

 Sc. and Arts, 1855, vol. 19, p. 133, 

 with Remarks by L. AGASSIZ, p. 136. 

 SCHULTZE, (M.,) Note sur le de- 

 vcloppeincnt des Petromyzous, Comp- 

 tes-Rendus, 1856, p. 336 ; Ann. and 



Mag. Nat. Hist., 2d ser., 1856, vol. 17, 

 p. 443. MULLER, (A.,) Ueber die 

 Entwickelung der Neunaugen, Miil- 

 ler's Arch., 1856, p. 303 ; translated 

 in Ann. Sc. Nat., 4e ser., 1856, vol. 5. 

 The unexpected facts mentioned here, 

 render it highly probable, that Am- 

 phioxus is the immature state of 

 some marine Cyclostorn. DUFOSSE, 

 De 1'hermaphrodisme chez certains 

 Vertebres, Ann. Sc. Nat., 4e ser., 1856, 

 vol. 5. 



1 The peculiarities of the develop- 

 ment of the Plagiostoms consist not 

 so much in the few large eggs they 

 produce, and the more intimate con- 

 nection which the embryo of some of 

 them assumes with the parent, as in 

 the development itself, which, not- 

 withstanding the absence of an 

 amnios and an allantois, closely 

 resembles, 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 obvious anatomical differ- 

 ences existing between the Pla- 

 giostoms and the bony Fishes, it 

 should be remembered, that, as in 

 the higher Vertebrata, 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 simply as an order in the 

 class of Fishes might even be in- 

 ferred from the fact, that they do 

 not constitute a natural series with 

 the other Fishes. I would, there- 

 fore, propose the name of SELA- 

 CHIANS for a distinct class, embracing 



