III. 



Its Value as a Study. 



We have seen in the first two lectures of the present 

 course what a very wide field of inquiry the science of 

 biology is now considered to cover. Indeed, any one of 

 its four main divisions of morphology, distribution, 

 physiology or aetiology constitutes a vast science in itself. 

 We saw how morphology dealt with the entire structure, 

 both gross and minute, of all animal and plant forms as 

 well as the relation of those structures to each other in 

 the organism. And, when we come to think of the 

 organic complexity of the great majority of the myriads 

 of different animals now living upon the earth, such a 

 task, alone, as unraveling their various plans of structure 

 would at first sight appear to be the labor of untold ages 

 for an infinite number of minds and hands. This un- 

 doubtedly would be the case were it not for the fact a 

 fact long since known to biologists that throughout the 

 entire series of animal forms and throughout the entire 

 series of plant forms, both living and extinct in either 

 case, and from the most simple type to the most complex, 

 there prevails the same fundamental uniformity in the 

 plan of structure. We may, for example, select any con- 

 venient form from the animal series, as a rabbit or a cat, 

 and after we have made a complete study of its entire 

 structure we have the key that unlocks the history of 

 the whole. From the cat, for instance, we may ascend 

 the scale, step by step, through the higher types, to in- 

 clude man himself, and it will be found that in the skele- 

 tons of all the bones are identically the same and require 

 but a common descriptive nomenclature. The viscera 

 and organs of the body are comparable throughout. The 

 arteries, veins, nerves and lymphatics in a cat, a lemur, 

 an ape and in man are strictly comparable, morphologi- 

 cally, and perform identically the same functions. There 

 are upward of 150 pairs of muscles or more in a cat, all 

 of which have been carefully described and named, yet 



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