196 THE HISTORY OF CREATION. 



Salamanders, giJled Salamanders, Csecilia, 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, etc. 



In conformity with this natural division of Amphibious 

 animals into two classes, the whole tribe of Vertebrate 

 animals was divided into two maia 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 Round-mouthed 



