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 I 



DIVISIONS OF THE ANIMAL KINGDOM. XX111 



relations with the world which they inhabit. In both king- 

 doms, we find not only an infinite diversity of organised 

 structures, but a passing from simple to more complex forms. 

 In the beings, the lowest in the scale of either kingdom, the 

 organs are few, or imperfectly developed. As we ascend in 

 the scale, further parts appear, further organs are called into 

 play, and further powers are given. At the lowest point, 

 the tribes of the two kingdoms seem allied, and proceed, as 

 it were, from a common root, and then progressively diverge. 

 In the simplest of plants, little can be discovered beyond a 

 series of minute cells. As we ascend in the scale, we find 

 tubes traversing this tissue, leaves unfolded, and other or- 

 gans called forth. So, in the animal kingdom, we find a pro- 

 gressive advance from simple to complex forms of structure. 

 At the limits of the descending scale are creatures so simple 

 in their organism, that they are scarcely to be distinguished 

 by the eye from plants ; and, like plants, they are fixed to 

 the spot which they inhabit. Ascending higher, we find 

 creatures with more expanded powers and more developed 

 organs, and so, in an ascending series, until we reach those 

 in which the highest development is presented to us of the 

 organs necessary for the exercise of the animal functions. 



By the term Species, naturalists designate those animals 

 which are essentially alike in themselves and their progeny. 

 The number of animal species is exceedingly great. Many 

 thousands have been examined and arranged by the unspar- 

 ing labour of naturalists ; thousands are known imperfectly ; 

 and thousands must for ever escape our observation. Of the 

 individuals comprehended under these species, the numbers 

 exceed our powers of conception. The air is alive with liv- 

 ing creatures ; every plant has its crowds of inhabitants ; and 

 all the waters of the sea and land teem with life. Numbers 

 of these creatures are so minute, that some hundred thou- 



nds may exist in a drop of water. 



In order to classify these innumerable forms of life, they 

 are arranged into Groups, the members of which agree in 



