GENERAL CHARACTERS OF MAMMALIA. 55 



in which they will display an intelligent adaptation of means to ends, with 

 the limited operations of Insects, over which the judgment and will seem to 

 have no control, we cannot help being struck with the difference. The former 

 are educable in the highest degree next to Man ; the latter could not be made 

 to change their, habits, in any essential degree, by the most prolonged course 

 of discipline ; still the difference, in this respect, between Man and the most 

 intelligent of other Mammalia, is so strongly marked, that some Naturalists 

 have proposed to exclude him altogether from the classification of this group, 

 and even from the Animal kingdom. This is, however, by no means a phi- 

 losophical plan; since the mind of Man is, in the present state of being, as 

 closely connected with its material tenement, as we have reason to believe that 

 of brutes to be ; and since there is scarcely any distinction of kind between their 

 faculties, which we have a right to assume as characteristic, the difference 

 being chiefly in degree ( 72). Man is like them actuated by instinctive pro- 

 pensities 7 , w r hich have an immediate bearing on his corporeal wants ; an^they 

 have, like him, the power of adapting their actions to gain certain feds, of 

 which they are conscious. A Dog or an Elephant may show more real wis- 

 dom, in controlling for a time its instinctive propensities, from the desire to 

 accomplish some particular object, than is displayed by many Men, wfco give 

 free scope to the exercise of their sensual passions, although warned by their 

 reason of the injurious consequences of such indulgence. 



54. This high development of the intelligence in Mammalia, is evidently 

 connected with the greatly prolonged connection between the parent and the 

 offspring, which we find to be a characteristic of this class. Mammalia are, 

 like Birds, warm-blooded Vertebrata, possessing a complete double circula- 

 tion ; and some of them are adapted to lead the life of Birds, passing a large 

 part of their time in darting through the air on wings, in pursuit of Insect 

 prey. But they differ from Birds in this essential particular, that they are 

 not oviparous, but viviparous, producing their young alive, that is, in a con- 

 dition in which they can perform spontaneous movements, and can appro- 

 priate nourishment supplied to them from without. But they are not dis- 

 tinguished from all other animals by this character alone ; for there are some 

 species among Reptiles, Fishes, and even Insects, which produce their young 

 alive, the egg being retained within the oviduct and hatched there. The 

 real distinction is that which the name of the class imports, the subsequent 

 nourishment of the young by suckling. There is another distinction, which 

 is not, however, equally applicable to the whole class. In all, the yolk-bag is 

 very small in proportion to its size in Birds ; and the contents of the ovum, 

 instead of furnishing (as in that class) the materials necessary for the develop- 

 ment of the young animal, up to the time when it can ingest food for itself, 

 only serve for the earliest set of changes in which this process consists. In 

 all the later stages of the evolution of the embryo, it is supplied with nutri- 

 ment directly imbibed from its parent. This is at first accomplished by means 

 oT a series of root-like tufts, which are prolonged from the surface of the 

 ovum, and insinuate themselves among the maternal vessels, without, how- 

 ever, uniting with them. These tufts absorb, from the maternal fluid, the 

 ingredients necessary for the support of the embryo ; and also convey back to 

 the parent its effete particles, which are received back into her blood, and cast 

 out of her system, by the processes of secretion, respiration, &c. 



55. The Mammalia may be divided into two sub-classes ; in one of which 

 the structure just described is the greatest advance ever made, in the appara- 

 tus by which the foetus is nourished ; whilst in the other, a more concentrated 

 form is subsequently assumed by it. The ovum of the latter is delayed for a 

 longer period, in a cavity formed by the union of the two oviducts, termed the 

 uterus : which can be scarcely said to be developed in the Marsupialia and 



