102 



MAMMALIA. 



of change, and many more resources in escaping 

 from it than any other animals. Hence, it has chiefly 

 been in the vegetable world that this yielding to circum- 

 stances in the individual plant has been verbally mag- 

 nified into a sort of doctrine of transmutation, where- 

 by, through the operation of a certain occult power 

 which has been gratuitously conjured up, under the 

 somewhat mystical name of development, roses may, 

 in their initial state, be changed into thorns (meaning 

 of course the spines on rose-trees) ; and, in certain 

 more elementary states, that which might have been 

 developed into a sea-plant, is developed into a land 

 one, and the reverse. 



It has also been maintained in the case of animals, 

 that there is a progress from the very simplest ; that 

 from those which appear to have no distinct organs>nd 

 which can be readily propagated by dividing their bo- 

 dies, up to the most perfectly organised animal, namely, 

 the human body, there is a progressive development ; 

 and it is inferred, and sometimes in great part said, 

 that, between the earliest rudimental embryo, and 

 the full growth of the animal, or rather our first per- 

 ception of it as an organised body, it must pass 

 through all these successive developments. They do 

 not of course fix the particular period of time during 

 which the higher animal, as we may call it, is in the 

 same condition as each of the lower ones through 

 which it must come in the successive stages of its 

 development. They do not, for instance, fix upon 

 the precise minute at which a horse, which is after- 

 wards trained to the turf, and wins the Derby or the 

 Oaks, is a snail, a black-beetle, a tortoise, a penguin, 

 or any thing else ; neither do they actually aver that 

 those developments take any measurable period of 

 duration between the very earliest embryo and the 

 final development of the specific animal ; but there is 

 a sort of dreaming belief upon the subject ; and as 

 dreams are said to occur only when the party is nei- 

 ther asleep nor awake, those philosophic dream?" or 

 to speak more correctly, those dreams about philo- 

 sophy are more mischievous than one would be apt 

 to suppose ; for they will neither allow the error 

 which they involve to slumber in oblivious repose, 

 nor bring it so completely before the awakened mind, 

 as that it can be detected and exploded. 



This is not the way of dealing with nature ; and 

 though we cannot be too orderly in the arrangement 

 of the facts of natural history, in that order in which 

 the one shall most easily bring the other to our recol- 

 lection, and where the connexion shall point where 

 the new one is to be discovered, all system beyond 

 the facts is mischievous ; for it is an attempt to work 

 without any materials. We can trace many of the 

 mammalia up to a very rudimental state ; arid in that 

 state it does not consist of so many organs visible to 

 our observation, or is it composed of parts apparently 

 differing so much from each other as these ; but still 

 whatever characters it has, are characters of its own 

 species and not of any other ; and as the progress of 

 its development (we may with perfect propriety use 

 this word when speaking of the evolvement of an 

 animal by the principle of animal life in itself, for this is 

 identical with the animal) ; as this progress advances, 

 we find invariably that the characters approximate more 

 and more to those of the full-grown individual of the 

 same species, unless under circumstances where we 

 can at least understand how there may have been a 

 deviation from the typical form, so that the individual 

 may appear mutilated or monstrous ; but it never 



does, nor can we suppose it ever could, assume the 

 characters of any other species. 



This is not exactly the place at which to speak of 

 deviations from the typical forms of species of mam- 

 malia ; but we are to bear in mind that the young 

 during the period of its growth has to work against 

 the pressure of the atmosphere, and that of the parts 

 by which it is surrounded ; and also as there are no 

 two individuals of any species absolutely alike, there 

 must be differences of development in the different 

 parts, arising from differences of strength and tone in 

 the young vessels, of which we can have no very 

 perfect knowledge. All this not only may be, but 

 must be, and probably is so in the case of every indi- 

 vidual animal, though the common cement is gene- 

 rally too early and obscure for us. This, however, is 

 only part of that play of the system which prevails 

 throughout the whole of nature, and without which, 

 indeed, the operations of a working world could not 

 be carried on. We shall not in the mean time, how- 

 ever, further prosecute this subject of diversity and 

 occasional deformity in the individual animal with 

 sufficient power to counteract the order of nature ; 

 but we shall briefly advert to those component parts 

 of the structure which are common to all mammalia. 

 It is not our intention, because it is not necessary 

 for the purpose of natural history, to enter into any 

 minute chemical exposition of the substances of which 

 the bodies of animals are composed The elements, 

 in the ultimate form to which they have been simply 

 analysed, are carbon, oxygen, hydrogen, and nitrogen, 

 with various alkalies and salts, ;md some slight quan- 

 tities of metals. These are differently compounded 

 in different tissues or textures of the body ; but no 

 connexion has been traced between the different che- 

 mical constitutions of the parts, and their different 

 uses in the economy of the animal. 



CELLULAR MEMBRANE may be considered as the 

 fundamental structure of the bodies of all the mam- 

 malia ; and that which holds all the other parts of 

 ! the different organs together, whether their cori- 

 | sistency be hard or soft. This, as its name imports, 

 consists of a multitude of small cells united together; 

 and it is found coating the most minute fibres of the 

 muscles, as well as ramified through the whole sub- 

 stance of the bones ; neither is there any vessel 

 within the body of an animal which is not embedded 

 in this membrane. Sometimes the cells are of con- 

 siderable extent, and readily filled with foreign mat- 

 ter ; as in the case of those surrounding and separating 

 the muscles, and also in many of those in the internal 

 parts of the body upon which fat accumulates ; but 

 those which surround the blood vessels are compact, 

 with the cells nearly obliterated. It does not appear 

 that this cellular membrane, or tissue, performs any 

 distinct function in the animal, but is more in the 

 character of a cement by which different parts are 

 ! united together. Our next object, therefore, is shortly 

 to notice the organs of motion. 



These consist of two classes movers, and sub- 

 ' stances immediately moved, though the moved sub- 

 i stance very often carries the mover along with it. 

 j The movers, or active parts in the body which ori- 

 ginate particular motions, and produce all the varied 

 actions of animals, are muscles, to which there are 

 various appendages, more numerous indeed in the 

 j structures of the mammalia than in those of any 

 \ other class of animals. These are cartilages, ten- 

 i dons, and ligaments, which answer the purposes of 



