NATURAL ORDER OF ANIMALS 



133 



VERTEBRATE ANIMALS. 



XI. Fishes. 



Oviparous, and without mammae ; respiration 

 complete and always by gills; two or four 

 primitive limbs ; fins for locomotion ; no hair 

 or feathers on the skin. 



XII. Reptiles. 



Oviparous, and without mammae ; respiration 

 incomplete, usually by lungs which exist either 

 throughout life or during the latter part of it ; 

 four Umbs, or two, or none ; no hair or feathers 

 on the skin. 



XIII. Birds. 



Oviparous, and without mammae ; four jointed 

 Umbs, two of which are shaped as wings ; respira- 

 tion complete, by adherent lungs, which are 

 pierced through ; feathers on the skin. 



XIV. Mammals. 1 



Viviparous, and possessing mammae ; four 

 jointed limbs, or two only ; respiration com- 

 plete, by lungs not pierced through ; hair on 

 some part of the body. 



K 



5th Stage. 



Nerves terminat- 

 ing in a brain which 

 is far from filling the 

 cranial cavity; heart 

 with one ventricle, 

 and the blood cold. 



6th Stage. 



Nerves terminat- 

 ing in a brain which 

 ' fiUs the cranial 

 cavity ; heart with 

 two ventricles, and 

 the blood warm. 



The above is a table of the fourteen classes of known animals arranged 

 in the order most in conformity with that of nature. The arrangement 

 of these classes is such that we shall always be obliged to adhere to it 

 even though we may refuse to adopt the lines of demarcation between 

 them ; because this arrangement is based on a study of the organisa- 

 tion of the living bodies concerned, and because this highly important 

 study reveals afl&nities among the objects comprised in each division, 

 and determines the rank of each division throughout the series. 



For these reasons no solid grounds can ever be found for changing 

 the general features of this classification, though changes may be 

 made as to detail, particularly in the divisions that are subordinate 

 to the classes ; because the affinities between the objects comprised 

 in the sub-divisions are more difficult to determine and leave more to 

 arbitrary opinion. 



Now in order to bring home more closely the conformity of this 

 arrangement of animals with the actual order of natiure, I shall set 

 forth the general series of known animals divided into its main groups, 

 proceeding from the simplest to the most complex according to the 

 principles indicated above. 



