THE LIFE OF ANIMALS. 



PRELIMINARY NOTES ON MAMMALS. 



However superficially the student or reader may 

 examine any subject, the necessity for some system 

 in the arrangement of the facts will at once be ap- 

 parent. This is especially true in connection with 

 investigation into the truths of nature, and more par- 

 ticularly those connected with our globe. The most 

 casual observer sees that the various natural objects, 

 each different from the other, align themselves into 

 larger and smaller groups having some one or more 

 characteristics in common. The systematic arrange- 

 ment of these classes, the division of them into 

 smaller groups, the proper classification of names 

 for these segregated assemblages of things, and the 

 orderly presentation of the facts in regard to these 

 divisions and the units of which they are composed, 

 constitutes, in broadly generalized terms, natural 

 science. 



In arranging the facts of nature that plan is best 

 which is simplest: and science has begun its work of 

 classifying the things on our globe by dividing them 

 into three primary groups called the Animal, Vege- 

 table and Mineral Kingdoms. Then, taking up the 

 classification of the Animal Kingdom and looking for 

 the first and most obvious division, it is found that 

 one large group of animals is made up of species 

 widely variant in other respects but agreeing in the 

 fact that each is possessed of what is popularly 

 known as a " backbone," consisting of a number of 

 segments of bone or cartilage jointed together, which 

 have been given the scientific name of " vertebrae," 

 the whole column of jointed segments being called 

 the " vertebral column." Therefore the Animal King- 

 dom has been scientifically divided into two sub- 

 kingdoms, known respectively as the Vertebrates 

 {Vertebrata) and, Invertebrates {Invertebrata), the 

 latter class including insects, mollusks, cephalo- 

 pods, worms, snails, animalcules, protozoa and other 

 classes of animals. 



The Vertebrates have several characteristics in 

 common besides the mere possession of a backbone. 

 Piercing the structure of the backbone is what is 

 known as the vertebral canal, enclosed by arches 

 of bone or cartilage forming part of the vertebrae, 

 this canal being the receptacle in which is stretched, 

 like a rope, the substance formed of nerve-tissue 

 which is popularly known as the spinal marrow or 

 spinal cord, and which is the main portion of the 

 nervous system of the animal. On the under side 

 of the backbone are placed the heart, the lungs and 

 the stomach and other organs of digestion. The 

 two jaws of Vertebrates are placed one above the 

 other instead of being right and left, as is the case 

 in insects, No vertebrate animal has more than four 

 legs, while some of the invertebrates have a very 

 large number. There are other physical character- 

 istics common to all, or nearly all. Vertebrates, but 

 their consideration involves technical explanations 

 which would be out of place here. 



Since Lamarck in 1797 suggested the division of 

 the Animal Kingdom into the two sub-kingdoms of 

 animals with and without backbones, this division 

 has been generally accepted. In the subdivision of 

 the Vertebrates there are usually recognized five 

 classes: the Mammals {Mammalia); the Birds {Aves)\ 

 the Reptiles (Reptilia); the Amphibious Animals, 

 like the Frog, Newt, etc. {Amphibia), and the Fishes 

 {Pisces). 



The Mammals, which form Class I. among the 

 Vertebrates, represent the highest forms of life on 

 our globe. Some have a much higher organization 

 than others, but still, from the highest to the lowest, 

 they have many characteristics in common. The 

 primary distinction upon which the class Mammalia 

 is founded, is the secretion in the glands ' of the 

 female of a fluid for the nourishment of her young 

 during the earliest period of infancy. In nearly all 

 of the animals of this class the fluid secreted is milk, 

 and the mammary glands are directly suckled by the 

 young, which are born alive and in a more or less 

 developed condition. I/i the lowest order of Mam- 

 mals, however, — the egg-laying Monotremes, — the 

 newborn, scarcely vitalized offspring is placed in a 

 pouch and there sustained by a nutritive perspira- 

 tion emitted from sweat-glands. In the order next 

 above them — the Marsupials — the development of 

 the animal at birth is only slightly more mature than 

 that of the Monotremes, and the pouch for maturing 

 the young places the infant in direct connection 

 with the mamma of the mother, which thus sup- 

 plies it with the milk needed to bring it to full 

 life and vigor. 



Mammals, besides being nurtured on mother's 

 milk in their infancy, are also characterized by the 

 possession of warm, red blood, circulated through 

 the system by means of veins and arteries leading 

 from a four-chambered heart. Every animal of the 

 mammalian class agrees with the other in possess- 

 ing a diaphragm membrane, or pleura, separating 

 the cavity of the chest from that of the abdomen. 

 For further statement of the general characteristics 

 of Mammals we quote from the introduction to the 

 German edition of Brehm's work, which says: "The 

 skull is separable from the vertebral column, or 

 backbone, in all Mammals; the upper jaw forms part 

 of the skull, and the teeth, though varying consider- 

 ably in number and shape, show that in common 

 they are in all species inserted in sockets. Seven 

 vertebrae usually go to form the neck, be it long, as 

 in the Giraffe, or short, as in the Mole. The chest 

 or thorax part of the vertebral column (known as 

 dorsal or thoracic vertebrae), consists of from ten to 

 twenty-four vertebrae; the lumbar vertebrae, or these 

 in the middle of the Isack, number from two to nine, 

 the sacrum has from one to nine and the tail from 

 four to forty-six. Ribs may be attached to differ- 

 ent vertebrae; but in speaking of ribs we usually 



