DIDELPHUS. 



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gestation of the ordinary mammalia and the internal 

 elaboration of the egg, and external, and we may say 

 unconnected evolution of the chick, by the process of 

 incubation, in birds. The common mammalia require 

 the interim! warmth, protection, and action of the 

 mother, with perfect exclusion of the atmosphere 

 from contact with the body during the whole time 

 that the fetus is coming into form. The bird requires 

 that the egg shall be matured in the ovary and oviduct 

 of the mother ; but when this is once accomplished, 

 the connection, that is, the material connection, 

 as conveying substance from the one to the other, is 

 cut off for ever as between the parent bird and the 

 future chick, which is still a formless embryo in the 

 egg ; so that the egg may be hatched, for the evolve- 

 mcnt of all the necessary membranes and vessels, and 

 the chick itself may be brought forward by the heat of 

 another bird, or by any heat, if properly applied. 

 We have therefore a second life, as it were, in the 

 young bird, in the action of which the parent bird has 

 no necessary concern ; and, if placed in favourable 

 circumstances, by the exclusion of atmospheric air and 

 the light, we know not for what length of time the 

 egg of a bird might not be preserved with the prin- 

 ciple of life within it, ready to be called into action 

 by the necessary stimuli, and capable of restoring the 

 species again to the world, even though, by any catas- 

 trophe, all the ancestors of the egg were swept away. 

 It is not so, however, with mammalia, for they would 

 necessarily perish, not only with the individual, but 

 with any circumstance which might affect the internal 

 health of the mother during the period of gestation. 



The marsupial animal is intermediate between 

 these ; and we may reasonably suppose, that as the 

 second stage of its progress in organisation takes 

 place externally of the mother, and partially exposed 

 to the atmosphere, we may very naturally conclude 

 that this marsupial foetus, being in less intimate con- 

 nexion with the system of its mother than an uterine 

 one, must not be so subject to suffer with the suffer- 

 ings of her system, but that the mother, with the 

 young in the marsupium, must be able to undergo 

 greater privations, and bear greater hardships, than 

 the uterine mother. We know, also, from the 

 observed fact, that a marsupial mother can bring 

 forward not only two, but perhaps three successions 

 of progeny at the same time. There have been found 

 some in the internal matrix, and some others in the 

 marsupium, so differing in size and development, that 

 they must have been the products of separate impreg- 

 nations. No doubt, we have cases of superfcetation 

 among uterine animals, as, for instance, in the common 

 hare, but the authenticated ones are very few in 

 number ; they are probably all referrible to the 

 category of " monstrosities of habit'' which take place 

 in animals, as well as monstrosities of form ; and, at 

 all events, they form the exception, and the rare 

 exception not. the rule. During marsupial gestation, 

 on the other hand, reimpregnation is so common, 

 as to be the rule, and not the exception ; and it 

 accords with the economy of nature that such should 

 be the case. There is, therefore, evidently an 

 absolvernent of the system of the marsupial female 

 from what would be called the labour of maturing the 

 succession, at that very time when this labour 

 falls most heavily upon the uterine mother, and 

 renders her more helpless than at any other state of 

 her mature and undecayed existence. 



Hence we see that the marsupial animal is fitted 

 for contending with, and triumphing over, hardships 



which the common mammalia eouSd not so well 

 endure ; and if, having found this power in the 

 animals, we can discover a corresponding occupation 

 for this power in the countries where such ai.inuds 

 are found, or in the situations in which they have to 

 preserve their lives and find their livings, then we are 

 in possession of two elements which will enable us 

 to approach at least to the outworks of this the most 

 impregnable point in the whole physiology of ani- 

 mated nature. 



Now, it will not fail to occur to every reader, who 

 has the slightest general acquaintance with the 

 economy and relative distribution of productions on 

 the surface of our earth, that the three grand localities, 

 or, strictly speaking, the two only, for New Holland 

 and the Oriental Isles, and south-eastern peninsula of 

 Asia, may be considered as one great district, which 

 is cut off from much migration of land-animals by the 

 intervening seas, but over which birds migrate with 

 the changing monsoons in numbers, which to us, 

 lying as we do at the outskirts even of the migration 

 of Europe, Western Asia, and Africa, would be 

 perfectly incredible, if we did not know the fact from 

 the most undoubted authority ; it will readily be seen, 

 that this tract, and also the eastern side of America, 

 which, from the great cordillera of the Andes running 

 near the west coast, comprises by far the greater part 

 of the continent, are countries beyond all others 

 stocked with tree birds ; and not only this, but that, 

 generally speaking, quadrupeds, with the exception of 

 these animals, are few, and of only trifling dimen- 

 sions. Australia, which, from the dryness of its surface 

 at one season, and the torrents in which rain falls at 

 others, may be regarded as having the extreme 

 character of this species of country ; and the qua- 

 drupeds there, with a few very trifling exceptions, 

 are all marsupial, whether they feed on animal matter 

 or on vegetable, and whether their chief prey be 

 sought on trees or on the ground. In South America 

 the character is less extreme, but still it is not less of 

 a tree-bird country than any part of the East, at least 

 in those regions which are covered, as much of it is 

 covered, with extensive and luxuriant forests. The 

 changes of season are very great in all those countries ; 

 and therefore, the labour which the animals have in 

 finding their food is sufficient to account for the 

 absolvement of the females from that portion of 

 systematic labour in bringing their young to maturity 

 which we have seen that they enjoy. This is not the 

 place for entering fully into the question ; but as all 

 the principal genera of marsupial animals occur in the 

 order of the alphabet before the general article 

 MARSUPIATA, we shall collect the leading points of 

 the evidence in the particular articles, which will 

 enable us to sum them up more briefly, and with a 

 better chance of being understood, than if we brought 

 a question so curious and so complicated into one 

 article. We shall therefore now resume our notices 

 of the species Didelphus. 



The CRAB-EATING OPOSSUM Didelphus Cancrivora, 

 This animal has more the figure of a rat than the 

 former. Its forehead is nearly straight, and its muzzle 

 much pointed. The general colour of the head is 

 white, with a few scattered bristly hairs, as whisker?, 

 on the upper lip and on the posterior part of the 

 cheek, and one or two over each eye ; the eyes and 

 ears are also black, which form a striking contrast 

 with the general white colour of the face and head. 

 The ground colour on the neck, the back, and sides, 

 is yellowish, sprinkled or grizzled with black and 



