24 THE PRESENT CONDITION 



mind's eye onward from the flapper of the Porpoise. And 

 here you have the hinder limbs restored in the shape of 

 these ventral fins. If I were to make a transverse section 

 of this, I should find just the same organs that we have 

 before noticed. So that, you see, there comes out this 

 strange conclusion as the result of our investigations, that 

 the Horse, when examined and compared with other 

 animals, is found by no means to stand alone in nature ; 

 but that there are an enormous number of other creatures 

 which have backbones, ribs, and legs, and other parts 

 arranged in the same general manner, and in all their 

 formation exhibiting the same broad peculiarities. 



I am sure that you cannot have followed me even in 

 this extremely elementary exposition of the structural 

 relations of animals, without seeing what I have been 

 driving at all through, which is, to show you that, step by 

 step, naturalists have come to the idea of a unity of plan, 

 or conformity of construction, among animals which 

 appeared at first sight to be extremely dissimilar. 



And here you have evidence of such a unity of plan 

 among all the animals which have backbones, and which 

 we technically call Vertebrata. But there are multitudes of 

 other animals, such as crabs, lobsters, spiders, and so on, 

 which we term Annulosa. In these I could not point out 

 to you the parts that correspond with those of the Horse, 

 the backbone, for instance, as they are constructed 

 upon a very different principle, which is also common to 

 all of them ; that is to say, the Lobster, the Spider, and 

 the Centipede, have a common plan running through their 

 whole arrangement, in just the same way that the Horse, 

 the Dog, and the Porpoise assimilate to each other. 



Yet other creatures whelks, cuttlefishes, oysters, snails, 

 and all their tribe (Mollusca) resemble one another in the 

 same way, but differ from both Vcrtchmtn and Annulosa ; 

 and the like is true of the animals called C&lcnterata 

 (Polypes) and Protozoa (animalcules and sponges). 



Now, by pursuing this sort of comparison, naturalists 

 have arrived at the conviction that there are, some 

 think five, and some seven, but certainly not more than 

 the latter number and perhaps it is simpler to assume 

 five distinct plans or constructions in the whole of the 

 animal world ; and that the hundreds of thousands of species 

 of creatures on the surface of the earth, are all reducible 

 to those five, or, at most, seven, plans of organization. 





