Ciup. I. SIZE OF ANIMALS. 47 



chiata especially; in the class of Cephalopoda, that of the Sepioids ; in the class of 

 Gasteropoda, that of the Nudihranchiata in particnlar; in the class of Acephala, that 

 of tlie Ascidiaiis and that of the Oysters in the widest sense; in the class of Echino- 

 derms, those of Holothiuna^ and Asterioids ; in the class of Acalephs, that of the 

 Hydroids ; in the class of Polyps, that of the Halcyonoids, of the Atrajoids, etc., etc., 

 deserve particnlar attention, and may be studied with great advantage in reference 

 to tlie points mider consideration. For everywhere do we observe in them, with 

 reference to space and to time, the tlioughtful combinations of an active mind. 

 liut it ought not to be overlooked, that Avhile some types represent strikingly con- 

 nected series, there are others in which nothing of the kind seems to exist, and the 

 diversity of which involves other considerations. 



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 relation 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. Tliis element of their 

 organization is not defined within those limits, though the Yertebrata, as a whole, 

 are larger than either Articulata, MoUusks, or Radiata; though Mammalia are larger 

 than Birds, Crustacea larger than Insects; though Cetacea are larger than Ilerljivora, 

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

 animals, size acquu-es a real importance, is that of families, that is, the groups ^\•hich 

 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 any- 

 where tenfold within these limits, and frequently only double. A few examples, 

 selected among the most natural families, ^vill show this. Omitting mankind, on 

 account of the objections which might be made against tlie idea that it embraces 

 any original diversity, let us consider the different families of Monkeys, of Bats, of 

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

 Birds, the \'ultures, the Eagles, the Falcons, the Owls, the Swallows, the Finches, the 

 Warblers, the Hmnming Birds, the Doves, the Wrens, the Ostriches, the Herons, 



