56 ON THE PLACE OF MAN IN THE SCALE OF BEING. 



Monotremata, the two orders constituting the first sub-class. The vascular 

 tufts proceeding from the chorion become especially developed at one point, 

 and the vessels of the uterus are extremely enlarged in a corresponding situa- 

 tion ; the tufts dip down, as it were, into a chamber formed by an extension of 

 the inner lining of these vessels, and serve the combined purpose of the roots 

 of plants and of the branchiae of aquatic animals, absorbing from the maternal 

 blood the materials required for the nourishment of the embryo, and aerating 

 that of the foetus by exposing it to the influence of the parents ( 749). The 

 peculiar organ thus formed is termed the placenta ; and the two sub-classes 

 of the Mammalia have thence received the appellations of placental and non- 

 placental. The animals belonging to the latter present many points of affinity 

 to Birds, in the structure of their internal organs. That of the brain is very 

 nearly allied in these two groups ; and their amount of intelligence seems, as 

 far as can be determined, to bear a close correspondence. The Ornithorhyn- 

 cus, in particular, has so many marks of alliance to Birds, in its osteology, as 

 well as in its horny bill, and in the spur on its hind leg (which resembles that 

 of the Cock), that Naturalists have much debated, whether it could really be 

 termed a Mammiferous animal. No positive evidence has yet been obtained, 

 that its young are born alive ; but on the other hand, there is a strong reason 

 to believe, that they come into the world unenclosed in the ovum, although in 

 a very imperfect condition. Moreover, it has been satisfactorily ascertained, 

 that the young are nourished, for some time after their birth, by a mammary 

 secretion, which the organization of their mouth at that period enables them 

 to obtain from the parent. In the Marsupialia, there is a remarkable compen- 

 sation for the abrupt termination of the period of uterine gestation, the young 

 being received into a pouch or marsupium, within which the nipple is situ- 

 ated ; this is extremely prolonged, and the mouth of the foetus (for so the 

 being must still be regarded) is adapted to receive and hold on by it ; so that 

 the little creature, which looks at first more like an earth-worm than a Mam- 

 miferous animal, is thus suspended within the protective pouch, until its 

 development is so far advanced, that it can shift for itself in the same degree 

 as other new-born animals can do. 



56. The period of gestation in the higher class of Mammalia, is usually 

 prolonged until the foetus is able, on its entrance into the world, to' execute 

 regular movements ; some of these being merely indicative of its desire for 

 food, and others evidently designed for the acquirement of it. In many species, 

 the young animal seems to be from the first in the full possession of its senses, 

 and has considerable power of active locomotion ; in general, however, it is 

 very dependent upon its parent ; only being able to obtain food, when this is 

 placed within its immediate grasp. Such is the case with the Human infant, 

 which is more or less closely dependent upon its parent, during a larger pro- 

 portion of its existence, than is the young of any other animal. Here, again, 

 therefore, we perceive the application of the general law, that, the higher the 

 grade of development a being is ultimately to assume, the more does it require 

 to be assisted during the early stages of its progress. In the case of Man, the 

 prolongation of this period has a most. important and evident influence upon the 

 social condition of the race ; being, in fact, one of the chief means, by which 

 the solitary are bound together in families. 



57. The class Mammalia, taken as a whole, is not characterized so much by 

 the possession of any one particular faculty, like that which has been seen 

 in Birds, as by the perfect combination of the different powers, which renders 

 the animals belonging to it susceptible of a much greater variety of actions 

 than any others can perform. There are none that can compete with Birds 

 in acuteness of sight ; but there are few that do not possess the senses of smell, 

 taste, and touch, in a more elevated degree. There are none which can rival 



