ZOOLOGY. 



greatest intelligence. They have a double circu- 

 lation, and warm blood, and breathe by lungs ; 

 but the air-tubes terminate in the air-cells of the 

 lung, and do not open on the surface of the lungs 

 as in birds. The skull is articulated to the back- 

 bone by two occipital condyles, and the cavities 

 of the thorax and abdomen are separated by a 

 partition or diaphragm, which is not the case in 

 birds. They produce their young alive, and 

 nourish them by a special fluid, the milk, secreted 

 by special glands the mammary glands, hence 

 the name of the class. Further, some part of the 

 skin is provided with hair at some period or other 

 of the animal's life. 



Naturalists, in seeking to classify the Mammalia, 

 have to look chiefly to those indications which the 

 teeth, extremities, and other external characters 

 furnish, regarding the general habits and disposi- 

 tions of the several animals. Thus, keeping out 

 of view minor distinctions, the possession of sharp 

 fangs and claws is a clear mark of carnivorous 

 habits ; flat-topped teeth and hoofs, equally a 

 proof of a gentle and herbivorous character. The 

 flapper of the whale shews a fitness for progres- 

 sion in the sea ; the development of a wing on 

 the hand of the bat, a design that the animal 

 should make its way through the air. 



Teeth are present in most of the Mammalia, 

 and their form, number, and mode of arrangement 

 yield important characters in the classification of 

 this class. In man and most mammals there are 

 two distinct sets of teeth one set which appears 

 shortly after birth, and which are termed the 

 milk or deciduous teeth, and a second set, which, 

 after a few years, replaces them, termed the per- 

 manent teeth. There are four kinds of teeth (per- 

 manent set) met with in the jaw of a typical 

 mammal, such as a dog. They are, the incisors, 

 which are implanted in the pre-maxillary bones, 

 and in the corresponding part of the lower jaw ; 

 the canines, or eye-teeth, those next to them in 

 order backwards ; the teeth which displace the 

 deciduous molars or grinders are called pre- 

 molars; and the most posterior teeth, which are 

 not displaced, are the true molars, which are not 

 represented in the deciduous set. For briefly 

 expressing the number of teeth in any mammal, a 

 dental formula is employed. The permanent 

 teeth in man are represented by the formula : 



2 ~ 2 C I 

 , \,. 



22 I I 



I T> 2 2 



P.--,M.3- 

 22 33 



32; 



where the letters stand for the four kinds of teeth 

 enumerated above, and where the two terms in 

 each nominator and in each denominator repre- 

 sent the number of each particular kind of tooth 

 in each half of the upper and lower jaw respect- 

 ively. All the teeth are implanted in distinct 

 sockets in the lower jaw. 



Owen classified this group according to the 

 structure of their brains, and De Blainville founded 

 his leading subdivisions upon the structure of the 

 reproductive organs. The Mammalia are prim- 

 arily divided into two sections : 



SECTION I. 



Implacentalia, including the following two orders, 

 where there is no vascular connection (placenta] 

 between the fcetus and the mother, and the young 

 are brought forth in a very immature state oi 

 development. 

 12 



ORDER i. The Monotremata (tnonos, single, 

 f rema, an aperture) so named because, as in 

 Dirds, the excretory organs are united into one 

 are exclusively Australian, and are represented 

 ay two genera. 



The Spiny Ant-eater (Echidna} is about the 

 size of, and somewhat resembles a hedgehog, has 

 a prolonged snout, and its back is armed with 

 spines. It has no teeth, and its food consists of 

 ants, which it entraps with its long adhesive 

 tongue. It is represented by two species (E. hystrix 

 and E. setosa}. The Ornithorhynchus (prnis, a bird, 

 and rygchos, a beak), or Duck Mole, is so called 

 "rom its bird-like snout. There is only a single 

 species, O.paradoxus. Its body is about the size of 



Duck-billed Platypus (Ornithorhynchus paradoxus}. 



a small otter, and is covered with dense fur. The 

 legs are short, and the feet have five toes each, 

 armed with strong nails suited for burrowing. 

 The toes are united by a web, so that the animal 

 can swim. It has no teeth, and its skull bears a 

 strong resemblance to that of a bird. It burrows 

 in the banks of tranquil rivers, and obtains its 

 food by the capture of small aquatic animals. 



ORDER 2. Marsupialia, or Pouched Animals 

 (marsupium, a pouch), derives its name from the 

 remarkable provision which is made for the young 

 after their immature birth. The skin of the 

 parent is so disposed as to form a pouch into 

 which the teats project, in which the immature 

 young are placed after birth, where they remain 

 attached to the teats until they acquire a degree 

 of development comparable to that with which 

 other animals are born. The angle of the lower 

 jaw is always turned inwards. 



The geographical range of this order is ex- 

 tremely peculiar. With the exception of the 

 Opossums, which inhabit America, its species are 

 at present almost confined to Australia and the 

 neighbouring islands, where they constitute, with 

 the Monotremata, almost the only mammifer- 

 ous animals. They have been divided by Owen 

 into families according to their predominating 

 food. 



(A.) Rhizophaga, or Root-eaters, as the Wom- 

 bat, which exhibits a curious resemblance to the 

 herbivorous Rodents in its dentition and in its 

 alimentary canal. The Wombat (Phascolomys 

 fossor) is about the size of a badger, by which 

 name it is known to the colonists, and is a 

 native of Tasmania. It is a sluggish and noc- 

 turnal animal, which burrows in the forests and 

 low grounds, and feeds upon the tougher kind of 

 vegetable substances. 



