While studjing the normal clevelopnient of Xecturus, the writer frequently noted that accidental wounds closed with astonishing rapidity. These observations gave a starting point for the following experimental study. The IarvE selected for the experiments were about 20-21 mm. in length. This stage was chosen because at this time the dermis is deeply pigmented over the dorsal surface and casual observations had shown that over this dark background certain light spots, presumably epidermal

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... res, moved toward the margin of the wounds. Each larva was placed in a solid match glass containing a bed of cotton, in the meshes of which it soon became entangled and was thus held in given position. A small piece of skin about 2 mm. long and 1 mni. wide was then cut from the mid-dorsal region. I n most of the experiments only the skin and subcutaneous tissues above the spinal cord were excisecl, yet in some, the spinal cord m s more or less injured. As soon as the excisions were made the l a r m were placed in separate dishes and examined either at short intervals, or continuously under the Zeiss binocular microscope with the No. a3 objective and the No. 4 oculars. Under this high magnification, one could readily follow the moveiiients of individual cells either remote from or at the margin of the cut. By this nieans it m s found that ihe deeply pigmented clerinal chroinatophores remained practically stationary while large irregularly scattered epidermal cells moved toward the margins of the \round. By following the movements of these cells which the study of sections shon-ed to be the unicellnlar gland cells, it was possible to determine the rate of movement of the epidermis over the dermis. Since the rate of movement was practically the S a m in all the experiments, it will suffice to illustrate the process by a single series of cliagrains which were taken at intervals Prom a single larra. On July 21, 9 a. in., AMERICAS JOLRXAL or ASATOXY.-VOL. VII.