I02 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



elsewhere. Even at this stage, before any morphological evidence of hy- 

 dranth development appears, it can be determined, from the presence of a 

 region of rapid reduction at one or at both ends of the piece, whether it 

 will develop as a unipolar or a bipolar form (Fig. 31).^ 



Electric-potential gradients have been observed in a considerable num- 

 ber of hydroids.'' Mathews, Hyman, and Bellamy and Child and Hyman 

 found apical levels galvanometrically electronegative to more basal levels. 



ABC 



Fig. 31, A-C. — Differential reduction of methylene blue in isolated pieces of Corymorpha 

 stem. A, bipolar form; B, unipolar with distal hydranth; C, unipolar with proximal hydranth. 

 Arrows indicate direction of progress of reduction (from Watanabe, 1935c). 



According to Lund, however, galvanometric positivity decreases from the 

 apical region basipetally and increases again toward the basal end of the 

 main axis of Obclia. Lund's data concern cut pieces without hydranths. 

 Barth docs not find uniformity of potential difference in different species 

 or in the same species under different conditions. The hydranth of Tubu- 

 laria is galvanometrically negative to middle levels, both distal and prox- 



* Child and Watanabe, 1935&; Watanabe, 193SC. 



9 Mathews, 1903, Parypha {Tuhularia), Pennaria, Canipamdaria; Hyman, 19206,- Hyman 

 and Bellamy, 1922, Tubiilaria crocea, Obelia geniculata, 0. borealis, Schizotricha lenella, Eiiden- 

 drium ramosum, Pennaria tiarella; Lund, 1922, 1923a, 19246, 1925, 1926; Rosene and Lund, 

 1930, 0. commisuralis; Child and Hyman, 1926, Corymorpha palma; Barth, 19346, Tuhularia, 

 Pennaria, Eudendrium. 



