The Physiological Gradients in Hydra I. Reconstitution and Budding in Relation to Length of Piece and Body Level in Pelmatohydra oligactis

T HE present paper is the first step in an attempted physiological analysis of hydra as an individual with particular reference to the significance of the polar gradient and includes data on reconstitution in relation to length and size of piece and level of the body, on rate of tentacle formation in relation to level, on susceptibility gradients in pieces, and on conditions determining formation and separation of buds. The presentation of data already in hand is reserved for subsequent papers. A review of the literature on hydra, particularly with regard to previous work on regeneration and reconstitution, seemed to indicate that a further study of this form from a quantitative standpoint and with the theory of the axial gradient in mind, might serve to give new meaning to results previously obtained as well as open up new lines of attack. Since Trembley's classic monograph of 1744 there has accumulated a widely varied and extensive literature relating to various fields of experimentation in hydra. These papers have been carefully summarized and reviewed by Koelitz (1910o) and Hyman (I927), and deal with lines of experimentation which are rather remotely related to those to be reported in this paper. It is well known that in some of the simpler animals the organism resulting from a piece following reconstitution often differs from the parent-animal in regard to morphological pattern. In Tubularia and Corymorpha forms have resulted ranging from unipolar (uniapical), bipolar (biaxial,heteromorphosis) to multipolar (multiapical) (Driesch, 1899; Morgan, 190o2, 1903; Child, 1926, etc.). Similar re-