198 THE HISTORY OF CREATION, 
tinguish them from the 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 
of 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. 
A. 
Skull-less Animals 1. Tubular hearts 1. Leptocardia 
(Acrania) 
a. Single-nostriled 
animals ‘e Round-months 2. Cyclostoma 
B. Monorrhina 
Animals with 3. Fish 3. Pisces 
Skulls b. Donble{ 1: Non- |4. Mud-fish 4. Dipneusta 
(Craniota) nostriled | A™nionate +5. Sea-dragons 5. Halisauria 
or animals Anamnia 1/6, Batrachians 6. Amphibia 
Thick Hearts | Amphir- 
(Pachycardia) rhina II. Amnion- (7. Reptiles 7. Reptilia 
ate. . Birds 8. Aves 
Amniota \9. Mammals 9. Mammalia 
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 
