The process of autotomy differs only in degree from the process of self-division. In autotomy the part thrown off does not produce a new animal. The breaking off of the tail of the lizard at the base, if the outer part is injured, is an example of a typical process of autotomy. The throwing off of the crab’s leg, if the leg is injured, is also another typical case of autotomy. There is a definite breaking-joint at the base of the crab’s leg at which the separation always takes place (Fig. 45, A 1-1). The breaking-joint is in the middle of the second segment from the base of the leg, where there is found, on the outside of the leg, a ring-like groove that marks the place of rupture. A comparison of the legs of the crab with the walking legs of the crayfish, or of the lobster, shows that the groove in the crab’s legs corresponds to a joint in the legs of the two other forms. In the crayfish and lobster the walking legs generally break off at this same level, although by no means as easily or with as much certainty as in the crab. The first pair of legs of the crayfish and lobster, carrying the large claws, have also a breaking-joint at the base of the leg similar to that in the crab’s leg, and these legs break off in the living animal always at the breaking-joint. [Illustration: FIG. 45.--_A._ After Andrews. Base of leg of crab to show breaking-joint, 1-1. _B._ After Fredericq. Diagram of leg of crab to show how autotomy takes place. _C._ After Andrews. Longitudinal section of base of leg to show in-turned chitinous plate at breaking-joint.]