Henslow also suggests that endogens have originated from exogenous plants through self-adaptation to an aquatic habit,[256] which is in line with our idea that certain classes of animals have diverged from the more primitive ones by change of habit, although this has led to the development of new class-characteristics by use and disuse, phenomena which naturally do not operate in plants, owing to their fixed conditions. Other botanists--French, German, and English--have also been led to believe in the direct influence of the _milieu_, or environment. Such are Viet,[257] and Scott Elliot,[258] who attributes the growth of bulbs to the "direct influence of the climate." In a recent work Costantin[259] shares the belief emphatically held by some German botanists in the direct influence of the environment not only as modifying the form, but also as impressing, without the aid of natural selection, that form on the species or part of its inherited stock; and one chapter is devoted to an attempt to establish the thesis that acquired characters are inherited. In his essay "On Dynamic Influences in Evolution" W. H. Dall[260] holds the view that-- "The environment stands in a relation to the individual such as the hammer and anvil bear to the blacksmith's hot iron. The organism suffers during its entire existence a continuous series of mechanical impacts, none the less real because invisible, or disguised by the fact that some of them are precipitated by voluntary effort of the individual itself.... It is probable that since the initiation of life upon the planet no two organisms have ever been subjected to exactly the same dynamic influences during their development.... The reactions of the organism against the physical forces and mechanical properties of its environment are abundantly sufficient, if we are granted a single organism, with a tendency to grow, to begin with; time for the operation of the forces; and the principle of the survival of the fittest." In his paper on the hinge of Pelecypod molluscs and its development, he has pointed out a number of the particular ways in which the dynamics of the environment may act on the characters of the hinge and shell of bivalve molluscs. He has also shown that the initiation and development of the columellar plaits in Voluta, Mitra, and other gasteropod molluscs "are the necessary mechanical result of certain comparatively simple physical conditions; and that the variations and peculiarities connected with these plaits perfectly harmonize with the results which follow within organic material subjected to analogous stresses."