Pseudo-autotomy in albino rat.

Abstract

Bayliss 1 describes the process of autotomy as follows: “If a crab be picked up by one of its ambulatory appendages, it generally, by a powerful contraction, breaks this leg off at a particular place and so obtains freedom. This mechanism was first investigated by Fredericq, and more recently by Raskam (1913). The second segment of the leg in the crab consists of two parts which are distinct members in most crustacea and united by a movable joint. In this animal, however, in place of a joint, there is a double membrane whose two components are not very firmly united. In the middle of the membrane there is an aperture, through which nerve and blood vessels pass. Certain muscles are so arranged that by a powerful contraction, they separate apart the two layers of the membrane. Thus no soft parts are torn, except the nerve and blood vessels; there is practically no bleeding and the peripheral part of the appendage is rapidly regenerated.”

A similar phenomena has long been known in some vertebrates. If a lizard is held by the tail it frees itself with a quick jerk at the expense of the piece of tail which remains in the hand. This phenomenon has also been termed autotomy, but it is different from true autotomy in that the tail itself is passive and is pulled apart, whereas muscles of the crayfish leg accomplish the separation which occurs there. At Dr. Carlson's suggestion, we wish to make manifest this difference by denoting as autotomy that mechanism by which an animal suddenly discards a portion of its body by a mechanism located in the member itself, and by denoting as pseudo autotomy that process by which an animal is enabled to {lose a portion of its body, the part king lost playing a merely passive rule. There is a possibility that such a portion of the body, the lizard tail, for instance, is especially adaptive (as to be unusually friable at a certain segment) for this purpose so as to facilitate the escape of the animal.