196 THE HISTORY OF CREATION. 
Salamanders, gilled Salamanders, Ceecilia, and the extinct 
Labyrinthodonta. Their entire organization is closely 
allied to that of Fishes. The Pholidota, or Reptiles, on the 
other hand, are much more closely allied to Birds. They 
comprise lizards, serpents, crocodiles, and tortoises, and 
the groups of the mesolithic Dragons, Flying reptiles, ete. 
In conformity with this natural division of Amphibious 
animals into two classes, the whole tribe of Vertebrate 
animals was divided into two main groups. The first main 
group, containing Amphibious animals and Fishes, breathe 
throughout their lives, or in early life, by means of gills, 
and are therefore called gilled Vertebrata (Branchiata, or 
Anallantoida). The second main group—Reptiles, Birds, 
and Mammals—breathe at no period of their lives through 
gills, but exclusively through lungs, and hence may appro- 
priately be called Gill-less, or Vertebrata with lungs 
(Abranchiata, or Allantoida). However correct this dis- 
tinction may be, still we cannot remain satisfied with it 
if we wish to arrive at a true natural system of the verte- 
brate tribe, and at a right understanding of its pedigree. In 
this case, as I have shown in my General Morphology, we 
are obliged to distinguish three other classes of Vertebrate 
animals, by dividing what has hitherto been regarded as 
the class of fishes into four distinct classes. (Gen. Morph. 
vol. ii. Plate VII. pp. 116-160.) 
The first and lowest of these classes comprises the Skull- 
less animals (Acrania), or animals with tubular hearts 
(Leptocardia), of which only one representative now exists, 
namely, the remarkable little Lancelet (Amphioxus lanceola- 
tus). Nearly allied to this is the second class, that of the 
Single-nostriled animals (Monorrhina), or Rouwnd-mouthed 
