THE 
AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[SECOND SERIES.] 
Art. XXVIII—On certain parallel relations between the classes 
of Vertebrates, and on the bearing of these relations on the question 
y the distinctive features of the Reptilian Birds; by James D. 
ANA, 
Ar the close of an article by Prof. Hitchcock, in this volume 
(p. 57), a portion of a letter of the writer is quoted, in which a 
screen is drawn between the Odtocoid or semi-oviparous 
ammals (Marsupials and Monotremes), the Ichthyoid Reptiles 
(Amphibians of DeBlainville, Batrachians of many authors), 
the Reptilian Birds. The general fact of this parallelism throws 
ght on (1) the classification of Mammals, (2) the distinctive 
ae of the Reptilian birds, and (3) the geological progress 
Or hie, 
_1. Classification —The Amphibians are made by many zoolo- 
ay an independent class of Vertebrates, on the ground of the 
h-like characteristics of their young. The same systematists, 
however, leave the Marsupials in the class of Mammals, not- 
withstanding their divergencies from that type. The number 
of classes of Vertebrates, usually regarded as four, thus becomes 
Jive, namely, Mammals, Birds, Reptiles, Amphibians and Fishes. 
There are some indications that this number will soon be further 
by some zoologists, through the making of another 
class out of the Reptilian Birds.’ 
* Professor iz, in vol. i of his Contributions to the Natural History of the 
United States, page 187, subdivides Fishes into four cl namely, 1, Myzonts; 
2, Fishes proper, or Teliosts (Ctenoids and Cycloids); 3, Ganoids ; 4, Selachians ; 
Which would make the total number of classes of Vertebrates nine, 
Am. Jour. Sct.—Srconp Serres, Vou. XXXVI, No. 108.—Nov., 1863. 
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