INTRODUCTION. ^ 



and whether it is in the womb, the nuirsupium, or the egg, its circulation, as soon as it has 

 one, as an entire system, is its own, and not part of that of the mother. The umbilical 

 cord is a substitute for feeding and breathing only ; and the pulse of the foetus is not con- 

 nected with, and does not beat at the same rate with that of the mother, and either may 

 survive the other, though the young in the early stages can do so only for a very short time. 

 Here, again, the details, interesting as they are, properly belong to physiology. 



The gradation of vertebrated animals may be considered as ranging from man to the 

 fishes ; and in the range there are four distinct classes very well denned, both by their 

 structure and their habits. BEASTS, BIRDS, REPTILES, and FISHES, are the common 

 English names of these four classes. The first of these is neither very descriptive nor very 

 precise in its meaning, as it is originally co-extensive with animal, or even with being ; and 

 therefore it is advisable to substitute for it the term MAMMALIA, which is strictly descriptive 

 of the most peculiar and distinguishing character of the class. 



INVERTEBRATED OR SPINELESS ANIMALS. 



Though these animals are all much smaller in size, and possess the principle of life in 

 what we are accustomed to call an inferior degree, their inferiority is of course merely relative; 

 because the structures of all animals, when considered with reference to the functions which 

 they perform, are equally perfect. But still, there is a very marked difference between the 

 two grand divisions of animals ; and, if the terms can be admitted, it may be said, that while 

 vertebrated animals are organised upon the brain and its spinal prolongation, as a basis, ths 

 invertebrated animals are organised upon the stomach, or the alimentary system. Not that 

 it by any means follows that these animals feed either more frequently or more Abundantly 

 than the vertebrated races; for many of them, in certain stages of their being, do not eat at 

 all, and in several, the functions of life, and feeding among the others, can be suspended for 

 years in all probability for ages without death ensuing. The resemblance which those 

 suspensions of the functions of life in the invertebrated animals bears to hibernation in tha 

 other classes has not been traced, and is, perhaps, not traceable ; but it may be stated as a 

 general fact, though one to which there are no doubt exceptions, that they obey the common 

 physical laws of matter much more readily than the vertebrated animals, being strongly 

 influenced, not only by climate and season generally, but by the slightest changes of the 

 weather, and even by the times of the day. 



It accords with general principles, that this greater obedience in the animal to the 

 common laws of matter should be the result of an inferior development of the principles of 

 animalisation ; for, in all the races with which we are most conversant, we invariably find that 

 the more sluggish life naturally is, it is the less easily extinguished. It must not, however, 

 be understood that this inferred or presumed inferiority in the invertebrated animals is 

 accompanied by a diminished intensity of any particular function. Indeed, it is rather the 

 reverse ; for the very same principle which enables the animal to yield more readily to 

 external circumstances must also enable the whole of its energy, so to speak, to go more 

 readily and completely to the performing of any one function. Accordingly, we find muscular 

 action and the endurance of mechanical injury so great in some invertebrated animals, that 

 we can hardly institute any comparison between them and the vertebrated ones. Comparing 

 the size, the grass upon the most finely mown lawn is apparently more formidable to many 

 insects than the closest jungle or forest would be to us. But the insect makes its way 

 easily and without fatigue ; and not only that, but it pushes aside substances as large in 

 comparison with its own bulk as if a man were to push the carts and waggons, nay almost 

 even the houses, out of his way as he walks the streets. If the spring of the lion, or the 

 bound of the antelope, wore to bear the same proportion to the size of those animals as that 

 N\T. HIST. VOL. I. 



