M A M MALI A. 



197 



seem, however, that a change takes place in those 

 organs, in the latter stage of the marsupial gestation ; 

 and that glands, capable of secreting milk, but differing 

 from the permanent mammary glands of the true 

 mammalia, are produced at the proper time for the 

 purposes of the young. 



That these glands are not conglomerate, like those 

 of all the land mammalia, which bring forth their 

 young alive, does not prove that they are not milk 

 glands ; for the mammary glands of the cetaceous 

 mammalia are not conglomerate, but consist of little 

 tubes which open at the one extremity, but are closed 

 at the other ; and in the cetacea the walls of these 

 are capable of secreting a milk which is as rich as 

 ordinary cream. It has been mentioned by several 

 observers in Australia, that these glands do contain 

 milk ; and that they appear sufficiently developed, 

 this milk is found in them, and can be extracted 

 from them by pressure, only at those stages of the 

 animal's economy, when the milk is necessary for the 

 young. 



Those observations have been made with such care 

 and reported with such accuracy, they have been 

 examined with so searching an analysis, and glands 

 analogous in situation to these, in shrews and some 

 other animals, have been shown to be developed at 

 times and for purposes eo different, that the fact of 

 the ornithorhynchus suckling its young, for some time 

 at least, may be said to be completely made out ; and 

 the establishment of this in the case of the ornitho- 

 rhynchus is tantamount to the establishment of it in 

 the case of the echidna. 



There still remains, however, the question of the 

 degree of development which the young have when 

 they leave the internal uterus. If they are in the 

 state of eggs, as we properly understand eggs in birds, 

 and in those oviparous reptiles which produce perfect 

 eggs, and do not hatch them internally, then there is 

 no instance of the contents of such an egg, when per- 

 fect, being incompetent to bring the contained an mal 

 to a state of maturity, if placed in the proper circum- 

 stances. It is true, that pigeons and some other 

 birds feed their young partially upon a secretion of 

 the stomach ; and that almost all birds, except such 

 as feed their young upon the most succulent and 

 easily digested food, prepare the food in part by the 

 lubricating and solvent juices, by means of which 

 they prepare their own food for the stomach. This, 

 however, is a very different operation from suckling, 

 and it is performed by a different apparatus, namely, 

 the common apparatus which the animal has for its 

 own feeding ; while the milk glands of the ornitho- 

 rhynchus are prepared for an express purpose, and at 

 an express time ; and therefore, whether the young 

 when brought from within are more or less developed, 

 or required to depend a longer or shorter time on the 

 mammary apparatus, we cannot, without violence to 

 the general analogy of nature, and the introduction 

 of organs for which there is no use, hesitate to admit 

 that the ornithorhynchus and the other monotrematous 

 animals follow the general law of the marsupial ani- 

 mals ; and differ from the others in adaptation to that 

 law only in so far as the fitting of them in the best 

 manser for their very peculiar habits is concerned. 



The following cut will furnish some idea of the 



figure of the ornithorhynchus when making its way 



through the water ; and we have added the foot on 



a larger scale, in order to show the curious manage- 



i mcnt of the web, by means of which this foot becomes 



alternately an efficient swimming and an equally effi- 

 cient digging instrument. It will be observed that 

 the web is capable of being stretched even beyond 



the extremities of the claws ; but it is also true that 

 it can be retracted, or turned upward upon the upper 

 side of the foot, so as to enable the animal to dig in 

 the earth with great force and activity, for which 

 purpose it is otherwise well adapted, in consequence 

 of the shortness, the strength, and the articulation of 

 its fore legs. In the quotation from Lieut. Maule, 

 the situation and form of the nest are described, so 

 that it is unnecessary to advert to these ; and it 

 should seem that the food, in great part at least, con- 

 sists of worms, and shell-less aquatic mollusca. The 

 echidna, on the other hand, being a land animal, and 

 having the mandibles and tongue differently formed, 

 is a feeder upon insects. Leaving, however, those 

 curious animals, we shall now very briefly advert to 

 the rest of the marsupial animals, in order that we 

 may trace the particular divisions of the common 

 mammalia to which they have the greatest resem- 

 blance. We have already offered some observations 

 on the opossums, and shown the correspondence 

 there is between them and the insectivorous division 

 of the common mammalia ; and the grand difference 

 in their habit is that the opossums are more the inha- 

 bitants of trees, and the insectivorous mammalia are 

 more the inhabitants of the ground. This throws 

 them upon different latitudes of the earth for their 

 pastures; the opossums being found in the American 

 continent only ; only one out of the warm latitudes, 

 and that one not reaching the cold ones ; while the 

 insectivorous mammalia which possess the three kinds 

 of teeth, and therefore range properly as carnassiers, 

 are most abundant in the temperate or the cold lati- 

 tudes ; and their place in the warm latitudes is sup- 

 plied by the ant-eaters and the analogous genera, 

 assisted by insectivorous reptiles, chiefly saurians, 

 whose structure and covering fit them for activity in 

 warm countries only. 



Simple as it may seem, there is a very beautiful 

 adaptation to other parts of nature, in this geogra- 

 phical distribution of those two classes of animals 

 Climbing insectivora would interfere with the summer 

 pastures of the birds in the deciduous groves and 

 forests of temperate countries, because the tree insects 

 and their larvae supply those birds with their proper 

 food ; and, on the other hand, animals constructed 

 like these ground mammalia would not be well 

 adapted for breaking open the strong castles of the 

 tropical ground insects, and levying such contribu- 

 tions upon the inmates as to preserve the proper 

 balance of the numbers. The soft-billed birds, and 



