KIDD'S LONDON JOURNAL. 



35 



happiness, but is a study which, it would be in- 

 excusable to neglect. 



A sketch of this nature should render prominent 

 the more general features of animal life, and de- 

 lineate the arrangement of the species according 

 to their most natural relations and their rank in 

 the scale of being; and thus give a panorama, 

 as it were, of the entire Animal Kingdom. To 

 accomplish this, we are at once involved in the 

 question, what is it that gives an animal preced- 

 ence in rank? 



In one sense, all animals are equally perfect. 

 Each species has its definite sphere of action, 

 whether more or less extended,— its own peculiar 

 office in the economy of nature; and is perfectly 

 adapted to fulfil all the purposes of its creation, 

 beyond the possibility of improvement. In this 

 sense, every animal is perfect. But there is a, 

 wide difference among them, in respect to their 

 organisation. In some it is very simple, and 

 very limited in its operation; in others, extremely 

 complicated, and capable of exercising a great 

 variety of functions. 



In this physiological point of view, an animal 

 may be said to be more perfect in proportion as 

 its relations with the external world are more 

 varied ; in other words, the more numerous its 

 functions are. Thus, a quadruped, or a bird, 

 which has the five senses fully developed, and 

 which has, moreover, the faculty of readily trans- 

 porting itself from place to place, is more perfect 

 than a snail, whose senses are very obtuse, and 

 whose motion is very sluggish. [This we have 

 elaborately shown in our " Treatise on Animal 

 Instinct."] 



In like manner, each of the organs, when sepa- 

 rately considered, is found to have every degree 

 of complication, and, consequently, every degree 

 of nicety in the performance of its function. 

 Thus, the eye-spots of the star-fish and jelly-fish 

 are probably endowed with the faculty of per- 

 ceiving light, without the power of distinguishing 

 objects. The keen eye of the bird, on the con- 

 trary, discerns minute objects at a great distance, 

 and when compared with the eye of a fly, is 

 found to be not only more complicated, but con- 

 structed on an entirely different plan. It is the 

 same with every other organ. 



We understand the faculties of animals, and 

 appreciate their value, just in proportion as we 

 become acquainted with the instruments which 

 execute them. The study of the functions or 

 uses of organs therefore requires an examination 

 of their structure; Anatomy and Physiology 

 must never be disjoined, and ought to precede 

 the systematic distribution of animals into classes, 

 families, genera, and species. 



In this general view of organisation, we must 

 ever bear in mind the necessity of carefully dis- 

 tinguishing between affinities and analogies, a 

 fundamental principle recognised even by Aris- 

 totle, the founder of scientific Zoology. Affinity 

 or homology is the relation between organs or 

 parts of the body which are constructed on the 

 same plan, however much they vary in form, or 

 serve for different uses. Analogy, on the con- 

 trary, indicates the similarity of purposes or 

 functions performed by organs of different 

 structure. 



Thus, there is an analogy between the wing 



of a bird and that of a butterfly, since both of 

 them serve for flight. But there is no affinity 

 between them, since, as we shall hereafter see, 

 they differ totally in their anatomical relations. 

 On the other hand, there is an affinity between 

 the bird's wing and the hand of a monkey, since, 

 although they serve for different purposes, the 

 one for climbing, and the other for flight, yet 

 they are constructed on the same plan. Accord- 

 ingly, the bird is more nearly allied to the mon- 

 key than to the butterfly, though it has the 

 faculty of flight in common with the latter. 

 Affinities, and not analogies, therefore, must 

 guide us in the arrangement of animals. 



Our investigations should not be limited to 

 adult animals, but should also be directed to the 

 changes which they undergo during the whole 

 course of their development. Otherwise, we 

 shall be liable to exaggerate the importance of 

 certain peculiarities of structure which have a 

 predominant character in the full-grown animal, 

 but which are shaded off, and vanish, as we revert 

 to the earlier periods of life. 



Again, we have a means of appreciating the 

 relative grade of animals by the comparative 

 study of their development. It is evident that 

 the caterpillar, in becoming a butterfly, passes 

 from a lower to a higher state ; clearly, therefore, 

 animals resembling the caterpillar, as, for instance, 

 worms, occupy a lower rank than insects. 

 There is no animal which does not undergo a 

 series of changes similar to those of the cater- 

 pillar or the chicken ; only, in many of them, 

 the most important ones occur before birth, 

 during what is called the embryonic period. 



The life of the chicken has not just commenced 

 when it issues from the egg; for, if we break the 

 shell some days previous to the time of hatching, 

 we find in it a living animal, which, although 

 imperfect, is nevertheless a chicken; it has been 

 developed from a hen's egg, and we know that, 

 should it continue to live, it will infallibly display 

 all the characteristics of the parent bird. Now, 

 if there existed in nature an adult bird, as im- 

 perfectly organised as the chicken on the day 

 before it was hatched, we should assign to it an 

 inferior rank. 



How very striking are the relations that exist 

 between animals and the regions they inhabit! 

 Every animal has its home. Animals of the cold 

 regions are not the same as those of temperate 

 climates; and these latter, in their turn, differ 

 from those of tropical regions. Certainly, no one 

 will maintain it to be the effect of accident that 

 the monkeys, the most perfect of all brute ani- 

 mals, are found only in hot countries; or that it 

 is by chance that the white bear and reindeer 

 inhabit only cold regions. 



Nor is it by chance that the largest of all 

 animals, of every class, as the whales, the aquatic 

 birds, and the sea-turtles, dwell in the water 

 rather than on the land; and while this element 

 affords freedom of motion to the largest, so is it 

 also the home of the smallest of living things. 



Such are some of the general aspects in which 

 we shall contemplate the animal creation. Two 

 points of view should never be lost sight of, or 

 disconnected, namely, the animal in respect to 

 its own organism, and the animal in its relations 

 to creation as a whole. By adopting too exclu- 



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