34 
VEKTEBRATA. 
m /:-/ 
Class I. MAmMAIilA. 
The highest boon conferred upon the lower animals 
is parental affection. The cold-blooded ovipara, reptiles 
and fishes, unable to assist in the maturation of their off- 
spring, are compelled to leave their eggs to be hatched by 
the agency of external circumstances, and their progeny, even from the moment of their birth, are 
usually abandoned to chance and their oavu resources for protection and nourishment. In birds, the 
duties and the pleasures inseparable froni the necessity of incubating their ova, and of providing 
nutriment for their callow brood, are indeed manifested to an extent altogether unparalleled in the 
lower order of vertebrate animals ; but it is to the mammals alone, the most sagacious and intelli- 
gent of all the inhabitants of the earth, that the Creator has permitted the full enjoyment of pater- 
nal and maternal love. It is in respect to these alone that he has cast the offspring absolutely 
helpless and dependent on a mother's care and solicitude, thus conferring upon the parent the joys 
and comforts that a mother only knows, the dearest, purest, and sweetest bestowed upon the ani- 
mal creation.* 
The grand circumstance, therefore, by which this class of beings, designated under the title of 
Mammalia, may be distinguished from all other members of the animal kingdom is, that the 
females of every species ai'e furnished with mammary glands — organs designed to supply a secre- 
tion called milk, whereby the young are nourished from the moment of their birth, until they 
have reached a sufficient age to enable them to live upon such animal or vegetable food as may be 
adapted to their mature condition. The possession of these lactiferous glands is the great and 
decisive characteristic of the class ; to this, however, it may be added, that their visceral cavity is 
separated into a thorax and abdomen by a muscular diaphragm, and that they breathe by means 
of lungs similar to our own. Of their internal structure, we shall give a more detailed example 
when we come to describe the human specie 
The mammalia are very widely distributed over the earth. Most of them are terrestrial in their 
habits, either browsing the herbage from the ground, or, if carnivorous, leading a life of rapine, by 
carrying on an incessant and destructive warfare against animals inferior to themselves in strength 
* Jones's "Structure of the Animal Kingdom." 
