V4 SCIENTIFIC AND LITERARY NOTES. 
fishes with well developed lung-like air-bladders (Polypterus, Lepidosteus, Sturio), 
and in the extinct reptiles, Archegosaurus and Labyrinthodon: the persistence of 
the notochord (chorda dorsalis) in Archegosaurus as in Sturio: the persistence 
of the notochord and branchial arches in Archegosaurus and Lepidosiren: the 
absence of occipital condyle or condyles in Archegosaurus as in Lepidosiren: the 
presence of teeth with the labyrinthic interblending of dental tissues in Dendrodus, 
Lepidosteus, ard Archegosaurus, as in Labyrinthodon; the large median and 
lateral throat-plates in Archegosaurus as in Megalichthys, and in the modern fishes 
Arapaima and Lepidosteus:—all these characters, as the author had urged in his 
Lectures at the Government School of Mines (March, 1858), pointed to one great 
natural group, remarkable for the extensive gradations of development, linking 
and blending together fishes and reptiles within the limits of such group. The 
salamandroid (or so-called “ sauroid”) Ganoids—Lepidosteus and Polypterus— 
are the most ichthyoid, the Labyrinthodonts the most sauroid, of the great group : 
the Lepidosiren and Archegosaurus are intermediate gradations, one having more 
of the piscine, the other more of the reptilian, character. Archegosaurus con- 
ducts the march of development from the fish proper to the Labyrinthodont type; 
Lepidosiren conducts it to the perennibranchiate, or modern batrachian, type. 
Both forms expose the artificiality of the ordinary class-distinction between Pisces 
and Reptilia, and illustrate the naturality of the cold-blooded Vertebrates, or 
“Hematocrya” (awa, blood, xpvos, frost: the correlative group is the “haemato- 
therma.”) Reptiles are defined as “ cold-blooded, air-breathing Vertebrates ;” 
but the Siren and Proteus chiefly breathe by gills, as did most probably the Arche- 
gosaurus. The modern naked Batrachia annually mature, at once, a large num- 
ber of small ova. The embryo is developed with but a small allantoic appen- 
dage, and is hatched with external gills. These are retained throughout life by a 
few species; the rest undergo a more or less degree of metamorphosis. Other 
existing reptiles have comparatively few and large eggs; and the embryo is in- 
closed in a free amnios, and is more or less enveloped by a large allantois. It 
undergoes no marked transformation after being hatched. On this difference the 
Batrachia have been by some naturalists separated as a distinct class from the 
Reptilia. But the number of ova simultaneously developed in the viviparous land 
salamanders is much less than in the siren, and not more than in the turtle; and, 
save in respect of the external gills, which disappear before or soon after birth, 
the salamander does not undergo a more marked transformation, after being 
hatched, than does the turtle or crocodile.* It depends, therefore, upon the value 
assigned 1o the different proportions of the allantois in the embryo of the sala- 
mander and lizard, whether they be pronounced to belong or not to distinct 
classes of animals. This embryonic, or developmental, character, is unascertain- 
able in the extinct Archegosaurus and Labyrinthodon. The affinity of Laby- 
rinthodon to Ichthyosaurus, and those structures which have led the ablest Ger- 
mans palzontologists to pronounce the Labyrinthodonts to be true Saurians, 
under the names of Mastodonsaurus, Trematosaurus, Capitosaurus, de. may well 
support the conjecture that modifications more “reptilian” than those in Sala- 
mandra may have attended the development of their young. Characters derived 
* The Cecilia may probably depart still further from the type-batrachian mode of 
development, and approach more to the type-reptilian mode. 
