318 Dana on Parallel Relations of the Ciasses of Vertebrates, 
It is plain from the preceding that the subkingdom of Verte- 
brates, instead of tailing off into the Invertebrates, has well-pro- 
nounced limits below, and is complete within itself. 
2. Distinctive features of the Reptilian division of Birds.—The 
skeleton of the fossil Bird, discovered at Solenhofen, has some 
decided Reptilian peculiarities, as pointed out by Wagner, Owen, 
and others. But even if perfect, it could not indicate all the 
Reptilian features present in the living animal. It is, there- 
fore, a question of interest, whether the relations of the hemi- 
typic to the typical species in the two classes, Mammals and 
Reptiles—one superior to that of Birds, and the other inferior— 
afford any basis for conclusions with regard to characteristics of 
the hemitypic Birds undiscoverable by direct observation. e 
following considerations, suggested by analogies from the classes 
just mentioned, may be regarded as leading to unsatisfactory 
foundly m in their young, they thus approximating in 
period of birth and some other respects to oviparous Vertebra 
B. Reptiles—(1.) The adult Amphibians, or hemitypie Rep- 
But (2.) the young, in their successive stages, from the egg 
“dab ke partake strikingly of characters of the inferior class of 
ishes. 
The law seems, then, to be that the species of the hemitypic 
group have their principal or most fundamental resemblance to 
those of the class or classes below in the young state. We 
red. | 
The characteristic of the intermediate type, on which the in- 
termediate character depends, is, in the case of both Mammt 
and Reptiles, that particular one which is the special distinction 
of the inferior type. The types inferior to Mammals are ovipa-_ 
rous, and hence the hemitypic Mammals are semi-oviparous. 
‘The type inferior to Reptiles, or that of Fishes, is distinctively 
_ aquatic and breathes consequently = Besse of gills instead ot 
~ Tongs, and hence the hemitypic Reptiles have gills in the young 
