Bronn's third factor in the production of variety of form is adaptation to environment, or better, functional response to environment. Bronn gives an excellent account of adaptational modifications and calls attention, just as Milne-Edwards did, to the numerous analogies of structure which adaptation brings about. He works out the interesting view that there is some connection between classificatory groups and adaptational forms, especially such as are connected with the function of locomotion:--"Based upon a common characteristic method of locomotion are whole or nearly whole sub-phyla (Hexapoda), classes (mammals and reptiles, birds, fishes, gastropods, pteropods, brachiopods, Bryozoa, Rotifera, jelly-fish, polypes, sponges), sub-classes (mobile and immobile lamellibranchs, echinoderms, walking and swimming Crustacea, parasitic and free-living worms, and so on), often, however, only orders and quite small groups (snakes, eels, bats, sepias, medusae, etc.)" (p. 141). It was characteristic of the 'forties and 'fifties that transcendental anatomy, along with Nature-philosophy, went rather out of fashion, its false simplicities and premature generalisations being overwhelmed by the flood of new discoveries. A few stalwarts indeed upheld transcendental views. We have already discussed the morphological system built up by Richard Owen in the late 'forties, a system transcendental in its main lines. We have seen the vertebral theory of the skull still maintained in the 'fifties by such men as Reichert and Koelliker, and we find J. V. Carus in 1853[314] taking it as almost conclusively proved.[315]