Studies on Transplantation in Planaria

DURING the last three years the writer has been engaged in a study of transplantation in Planaria. The object of this DURING research was, first, to determine the effect or influence of the graft on the host and of the host on the graft; and second, to determine how the different levels or regions of the body of Planaria differ (a) as host and (b) as graft. The investigation was suggested by Dr. C. M. Child, and the work has been carried on under his direction. The writer wishes to acknowledge his indebtedness to Dr. C. M. Child for suggestions and criticisms. Some of the questions that arose in the course of this investigation and furnished additional stimulus in the carrying-out of this research are: (i) Does the fate of the graft depend upon the degree of specialization, or does it depend upon the degree of physiological activity of the graft? (2) Does the active dominant region of the planarian body, such as the head or ganglionic region of the head (Child, 1929b), act as an organizer when transplanted into a relatively less active region of the body? (3) Is its effect species-specific? (4) On what factors does the fate of the graft depend? The work was undertaken in the hope of throwing additional light on the dynamics of histogenesis and of morphogenesis. Some of the more important results obtained thus far have already been briefly discussed in the preliminary paper (Santos, 1929). Most of the earlier work on transplantation in the lower invertebrates has been chiefly concerned with other problems than those which are attacked in the present paper. Various investigators have grafted together pieces of hydroids, Turbellaria, or annelids in various positions. When such grafts are made in reversed polar orientation with respect to each other and one component is made much