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Reptilian and Amphibian Motions.—M. Marey has extended his time-photographic studies of locomotion to mammals, birds, reptiles, fishes, and articulates. The processes are rather difficult, because they have to be applied to a great variety of movements, and of methods and habits of carrying them on; but it is nearly always possible to assure satisfactory representations by adapting the methods of working to the conditions. The chief difficulty is in getting the animal experimented upon to go at its ordinary gait. This is much more easily accomplished with domesticated animals than with wild ones. By comparing the types which he has got represented, M. Marey discovered some very interesting analogies. Thus, in locomotion on land and on water, he was able to follow the gradual transition between simple "reptation" and the most complicated kinds of locomotion. An eel and a viper, put in water, advance in the same manner; a wave with lateral inflections runs continuously from the head to the tail of the animal, and the velocity of the retrograde movement of the wave is much greater than the speed of translation of the animal. If the animals are set upon the ground, the mode of reptation will be modified in both in the same way. The amplitude of the undulatory movement from one side to the other will be greater, and will increase as the surface on which the animal creeps is smoother. A vestige, more or less pronounced, of the undulatory reptilian movement remains with fish that have fins and reptiles endowed with legs. In the sea-dog, for instance, the retrograde wave running along the whole body is very pronounced. It is considerably reduced in the salmonides, and does not appear except at the tail in fishes the bodies of which are more stubby. This retrograde wave is plainly manifest in the gecko, but less so in some other lizards. The analysis of the varieties of locomotion of the batrachians in the different stages of their evolution is very interesting. The tadpole, for example, exhibits in its earliest stage progression by the undulation of the caudal fin; a mixed type of locomotion comes in with the paws; the tail continues to wriggle, and the hinder limbs make the swimming motions appropriate to them; and the latter movements exist alone for some time after the tail has disappeared. These motions, which so much resemble those of man's swimming, present the peculiarity of the fore legs having no part in them, and of the hind legs, after having been separated so widely as to form a right angle with the axis of the body, approaching one another till they become parallel, then bending and spreading out again to begin a new spring. The motions of lizards' legs are so swift as to escape direct observation, but the successive movements of the fore and hind limbs can be followed in photographs taken forty or fifty times a second. The normal gait of the lizard and the gecko is the trot—that is, their limbs move diagonally. The great amplitude of the motions, combined with the undulation of the axis of the body, causes the limbs on the same side to come very near one another, and then separate widely in the following instant. The lizard projects its hind foot nearly into its armpit on the side on which the body becomes concave; an instant afterward that side becomes convex, the fore leg is carried far forward, and, the body forming a convex arc on that