So, too, the embryologists after Cuvier often came across instances of the special formation of parts to meet temporary needs. Thus Reichert interpreted the "palatine" and "pterygoid," which are formed in the mouth of the newt larva by a fusion of conical teeth, as special adaptations to enable the little larva to lead a carnivorous life.[310] Not many years after the publication of Milne-Edwards' _Introduction a la zoologie generale_ (1851) there appeared a book by H. G. Bronn in which was offered a very similar analysis of organic diversity. The curious thing was that Bronn approached the problem from quite a different standpoint, from the standpoint, indeed, of _Naturphilosophie_. Of this the title of the book is itself sufficient proof--_Morphologische Studien ueber die Gestaltungs-gesetze der Naturkoerper ueberhaupt und der organischen insbesondere_ (Leipzig and Heidelberg, 1858).[311] The linking up of organic with inorganic form is characteristic; there is much talk, too, in the book of _Urstoffe_ and _Urkraefte_, but underlying the _Naturphilosophie_ we can trace the same Cuvierian treatment of form, and see crystallise out laws of progressive development that bear no small analogy with the laws established by Milne-Edwards. According to Bronn, the ideal fundamental form of the plant is an ovoid or strobiloid[312] body, for a plant reaches out in two directions in search of food--towards the sun and towards the earth. Animals differ from plants in being endowed with sensation and mobility (_cf._ Aristotle and Cuvier), and it is this characteristic that gives them their distinctive form. The main types of animal form--the Amorphozoa, Actinozoa, and Hemisphenozoa--are essentially adaptations to particular modes of locomotion. Animals either are fixed, or they move in all directions without reference to any definite axis, or they move in one main direction. The Amorphozoa or shapeless animals include many of the Protozoa and sponges; they have no typical form, and most of them are sessile. The Actinozoa include such animals as the Coelentera, which are fixed, and the Echinoderms, which have a central point and move indifferently along any radial axis; their form differs from the strobiloid mainly in having radiate rather than spiral symmetry. The Hemisphenozoa, or bilaterally symmetrical animals, include all those that habitually move forward; they have a front end and a hind end, a dorsal surface and a ventral, and the mouth, sense-organs and "brain" are concentrated in the front end to form a head--all in direct adaptation to this forward movement; they make up the vast majority of animals.