194 



MAMMALIA. 



the other localities of these animals. New Holland, 

 New Guinea, some of the other islands of the archi- 

 pelago, South America, and the warmer part of North 

 America, in the case of a single species only, are 

 the localities of these animals ; and it is not a little 

 remarkable that not one of them hasbeen hitherto 

 found in Africa, though they occur on both sides 

 of it. 



As they have their portion of the earth set apart 

 for them as it were, they are distributed into their 

 own orders, which, however, have been usually taken 

 into the system as genera, and perhaps it is not worth 

 while to alter an arrangement which cannot be mis- 

 understood, if we do not confound them with the 

 other mammalia. 



The singular part of the economy of these animals 

 is, however, the pouch, and the double gestation. 

 There has been much inaccurate writing on this sub- 

 ject, but the leading facts have been in a great mea- 

 sure cleared up. The Virginian opossum, which has 

 been longest known, has been examined with a good 

 deal of attention. From which it appears that the 

 pouch begins to be visibly preparing for the young 

 about the tenth da)', and that in about five days more 

 the young are placed in it. This is done always in 

 a state of concealment, and consequently the exact 

 method of it is not known, though there is no doubt 

 the mouth is the instrument. When these young are 

 deposited in the pouch they are very small, not ex- 

 ceeding a grain or two in weight. The mother, it is to 

 be borne in mind, is about the same size as a common 

 domestic cat. On the twenty-fifth day the motion of 

 the young in the pouch is sufficiently great to be felt 

 by the finger on the outside ; and by eight or nine 

 weeks the young ones are found hanging, some with- 

 out and some within the pouch. While they continue 

 suspended to the nipple it is about a quarter of an 

 inch long ; but they do not quit the teats till they 

 are about the size of rats. After this the teats 

 begin to shrivel up and soon disappear. About the 

 eighth week the eyes are opened, at which time they 

 begin to quit the teats, though they return to them 

 for some short time. 



The marsupial bones, which are found in the 

 skeletons of no other animals, form a very peculiar 

 character. They are inserted by a tendinous union, 

 and not by joints near the middle of the pubis, and 

 directed towards the sides ; and it does not appear 

 that there is any necessary correspondence between 

 the development of the bones and that of the pouch 

 in its soft parts. The males have them as well as the 

 females and those which have the pouch but very 

 little produced, have often the bones very decidedly 

 so. Though the pouch and its economy be the most 

 remarkable, they are not the ones upon which it is 

 convenient to divide the animals, the proper mode of 

 division being the teeth and feeding apparatus, as in 

 i'.ie case of the mammalia properly so called. But 

 whatever may happen to be the food or teeth of these 

 animals, and whether the pouch is well developed or 

 merely rudimental, there is a family likeness which 

 runs through the whole. The animals never have 

 the graceful form of the true mammalia ; they have a 

 very stupid look and expression in comparison to 

 these, and they are sadly inferior to them in resources, 

 though their dispositions are generally mischievous 

 enough in proportion to their strength. 



In the marsupial animals, and particularly in those 

 of them which have the marsupial character most 



completely developed, there are certain conformations 

 of the blood-vessels in the lower part of the body, in 

 which they differ from the mammalia. These conforma- 

 tions tend to secure, in proportion to the blood of the 

 whole animal, a greater supply of arterial blood to 

 the lower extremities, and to those parts in which the . 

 peculiar characters of the animals are situated. The 

 marsupimn and its bones render the pelvis deeper 

 than it is in any of the mammalia, and this enables the 

 iliac branches to come off earlier and at smaller an- 

 gles, by which means the blood circulates more freely 

 and in larger quantity, and this supplies the waste of 

 the more powerful action of the hind legs, and, gene- 

 rally speaking, also of the tail. Those peculiarities 

 cannot be very clearly explained, however, without 

 the assistance of figures, and not easily to ordinary 

 readers with them. 



The spine and skull do not differ greatly from those 

 of the common mammalia in the arrangement of their 

 principal parts, only in the more characteristic species, 

 the skull is smaller in proportion, and the vertebral 

 column is enlarged towards its sacral extremity. The 

 fore legs are always furnished with complete cla- 

 vicles, and thus they have always a cross motion, so 

 that the animal can grasp with them or bring them to 

 the mouth. In their development the organs of 

 sense follow nearly the same law of adaptation to 

 locality as is found in the mammalia ; but the fore 

 paw has in no case less than four fingers and a rudi- 

 mental thumb. Some of them, however, have the fore 

 feet adapted for digging in the ground ; one or two 

 have the toes of all the feet webbed, and several have 

 the hind feet formed like those of the leaping ani- 

 mals. Some of them, as the koala, have the toes of 

 each foot divided into two groups, an external one 

 containing three, and an internal one containing four, 

 which act against each other in grasping. In those 

 which simply run upon the ground, and which are 

 more or less of a carnivorous character, the feet ap- 

 proach more to those of the running carnivora, having 

 five toes on the fore feet and four on the hind, all 

 armed with claws which are sharp and crooked, but 

 not retractile. The whole race are, with but few ex- 

 ceptions, solitary animals, living alone, and rarely 

 found in more than a single pair, and that only occa- 

 sionally. The kanguroos are almost the only ones 

 which form an exception to this ; and they make a 

 slight, though a very slight, approach to the rumi- 

 nant mammalia in their food, and the fact of their 

 being of some use to man ; but the approach is but 

 a slight one, and their social principle is not suffici- 

 ently strong for admitting of their being tamed. 



We shall now very shortly notice the several 

 genera, or, perhaps, to speak more accurately, orders 

 or sub-orders into which these animals are usually 

 divided. The first are the opossums, which are 

 wholly American animals, though some are furnished 

 with a pouch and others not, and one at least is 

 aquatic in its habits. These animals have their 

 mouths formed very like those of the insectivorous 

 mammalia. They have ten front teeth above and 

 eight below, which last are very small ; one canine 

 tooth in each side of both jaws, which is strong and 

 compressed ; and seven cheek teeth in each side of 

 both jaws, the ones next the canines very small, and 

 the otiiers with pointed tubercles like all insectivo- 

 rous teeth. The head is long, the muzzle pointed, 

 the gape wide, the ears rounded and nearly destitute 

 of hair, and the tongue studded with hard poinU 



