156 ESSAY ON CLASSIFICATION. Part I. 



body to one another. Cuvier speaks of form in general with reference to these 

 four great types as a sort of mould, as it were, in which the different types 

 would seem to have been cast. Again, form is alluded to in characterizing orders; 

 for instance, in the distinction between the Brachyourans and the Macrourans among 

 Crustacea, or between the Saurians, the Ophidians, and the Chelonians. It is men- 

 tioned as a distinguishing feature in many famiHes, ex. gr. the Cetacea, the Bats, 

 etc. Some genera are separated from others in the same family on the ground 

 of differences of fonn; and in almost every description of species, especially when 

 they are considered isolatedly, the form is described at full length. Is there not, 

 in this indiscriminate use of the term of form, a confusion of ideas, a want of 

 precision in the estimation of what ought to be called form and what might be 

 designated by another name? It seems to me to be the case. In the first place, 

 when form is considered as characteristic of Radiata or Ai'ticulata, or any other 

 of the great tyjjes of the animal kingdom, it is evident that it is not a definite 

 outhne and well-determined figure which is meant, but that here the word fonn 

 is used as synonym for plan. Who, for instance, would describe the tubular body of 

 an Holothuria as characterized by a form similar to that of the Euryale, or that of 

 an Echinus as identical with that of an Asterias? And who does not see that, as 

 far as the fonn is concerned, Holothui'iaj resemble Worms much more than they 

 resemble any other Echinodenn, though, as far as the plan of their structure is 

 concerned, they are genuine Eadiates, and have nothing to do with the Articu- 

 lates ? 



Again, a superficial glance at any and all the classes of the animal kingdom 

 is sufficient to show that each contains animals of the most diversified forms. 

 What can be more different than Bats and Whales, Herons and Parrots, Frogs and 

 Sirens, Eels and Turbots, Buttei'flies and Bugs, Lobsters and Barnacles, Nautilus 

 and Cuttlefishes, Slugs and Conchs, Clams and compound Asidians, Pentacrinus and 

 Spatangus, Beroe and PhysaUa, Actinia and Gorgonia ? And yet they belong respec- 

 tively to the same class, as they are coupled here : Bats and Whales together, 

 etc. It must be obvious, then, that form cannot be a characteristic element of 

 classes, if we would understand any thing definite under that name. 



But form has a definite meaning miderstood everywhere, when applied to weU- 

 known animals. We speak, for instance, of the human form ; an allusion to the 

 form of a horse or that of a bull conveys at once a distinct idea; everybody would 

 acknowledge the similarity of form of the horse and ass, and knows how to distin- 

 guish them by their form from dogs or cats, or from seals and porpoises. In this 

 definite meaning, fonn corresponds also to what we call figure when sj^eaking of 

 men and women, and it is when taken in this sense, that I would now consider 

 the value of forms as characteristic of different animals. We have seen that form 



