198 



THE HISTORY OF CREATION. 



tinguish them from tlie two lowest classes (the single- 

 nostriled and tubular-hearted animals). Hence we may unite 

 them in the natural main group of Double-nostriled animals 

 (Amphirrhina). Finally, these Amphirrhina on the whole 

 are much more closely related to those animals with round 

 mouths or single nostrils than to the skull-less or tube- 

 hearted animals. We may, therefore, with full justice class 

 the single and double-nostriled animals into one principal 

 main group, and contrast them as animals with skulls 

 (Craniota), or bulbular hearts (Pachycardia), to the one class 

 f)f skull-less animals, or animals with tubular hearts. This 

 classification of the Vertebrate animals proposed by me 

 renders it possible to obtain a clear survey of the nine 

 classes in their most important genealogical relations. The 

 systematic relationship of these groups to one another may 

 be briefly expressed by the following table. 



SfeuII4css 'Inintals 

 (Acrania) 



B. 



Animals Snitlj 



Shulls 



(Craniota) 



or 



VL%itk l^earts 



(Pachycardia) 



a. Single-nostriled 



animals 



Monorrhina 



h. Double 

 nostriled 

 animals 

 Amphir. 

 rhina 



I. Non. 

 Amnionate 

 Anamnia 



II. Amnion- 

 ate. 

 Amniota 



1. Tubular hearts 1. Leptocardia 



2. Round-mouths 2. Cyclostoma 



/3. Fish 3. Pisces 



4. Mud-fish 4. Dipneusta 



I 5. Sea -dragons 5. Halisauria 



I 6. Batrachians 6. Amphibia 



(7. Reptiles 7. Reptnia 



! 8. Birds 8. Aves 



i 9. Mammals 9. MammaHa 



The only one representative of the first class, the small 

 lanceolate fish, or Lancelet (Amphioxus lanceolatus) (Plate 

 XIII. Fig. B), stands at the lowest stage of organization 



