54 ESSAY ON CLASSIFICATION 



SECTION XIII 



RELATION BETWEEN THE SIZE OF ANIMALS 

 AND THEIR STRUCTURE 



The relation between the size and structure of animals has been 

 very little investigated, though even the most superficial survey of 

 the animal kingdom may satisfy any one that there is a decided rela- 

 tion between size and structure among them. Not that I mean to 

 assert that size and structure form parallel series, or that all animals 

 of one branch or even those of the same class or the same order agree 

 very closely with one another in reference to size. This element of 

 their organization is not defined within those limits, though the 

 Vertebrata, as a whole, are larger than either Articulata, Mollusks, 

 or Radiata; though Mammalia are larger than Birds, Crustacea larger 

 than Insects; though Cetacea are larger than Herbivora, these larger 

 than Carnivora, etc. The true limit at which, in the organization of 

 animals, size acquires a real importance is that of families, that is, 

 the groups which are essentially distinguished by their form, as if 

 form and size were correlative as far as the structure of animals is 

 concerned. The representatives of natural families are indeed closely 

 similar in that respect; the extreme differences are hardly anywhere 

 tenfold within these limits and frequently only double. A few exam- 

 ples selected among the most natural families will show this. Omit- 

 ting mankind, on account of the objections which might be made 

 against the idea that it embraces any original diversity, let us con- 

 sider the different families of Monkeys, of Bats, of Insectivora, of 

 Carnivora, of Rodents, of Pachyderms, of Ruminants, etc., among 

 Birds, the Vultures, the Eagles, the Falcons, the Owls, the Swallows, 

 the Finches, the Warblers, the Humming Birds, the Doves, the 

 Wrens, the Ostriches, the Herons, the Plovers, the Gulls, the Ducks, 

 the Pelicans; among Reptiles, the Crocodiles, the different families 

 of Chelonians, of Lizards, of Snakes, the Frogs proper, the Toads, 

 etc.; among Fishes, the Sharks and Skates, the Herrings, the Cod- 

 fishes, the Cyprinnodonts, the Chastodonts, the Lophobranchii, the 

 Ostracionts, etc.; among Insects, the Sphingoidas or the Tineina, the 

 Longicorns or the Coccinellina, the Bomboidas or the Brachonidas; 



