98 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



agree in indicating a single gradient with high end apical (Fig. 30, A). 

 Somewhat later a secondary gradient appears at the basal end but re- 

 mains short (Fig. 30, B) and becomes the region of holdfast origin (Fig. 

 30, C), while the hydranth develops at the primary apical end. 



Determinations of oxygen uptake, comparative estimations of CO^ pro- 

 duction, differential reduction of methylene blue and permanganate, and 

 electric-potential differences all give evidence of gradient pattern in adult 

 hydrozoa. Corymorpha palma is exceptionally favorable material for re- 



\^ 



Fig. 30, A-C. — Development of the hydrozoan Corymorpha palma from early planula. .4, 

 early planula with single basipetal gradient; B, later planula with secondary acropetal gradient 

 in basal region; C, young hydroid, primary gradient becomes hydranth-stem axis (from Child, 

 1925a). 



spiratory determinations because of large size — it may attain a length of 

 10-12 cm. — and because of absence of perisarc over most of the stem 

 length and complete absence of branches.^ Determinations of oxygen up- 

 take at different levels of the naked stem region are given in Table 3, and 

 comparative data on CO^ production in Table 4. 



Other CO2 estimations showed a much higher rate in hydranth than in 

 stem, and in short distal than in short middle pieces. The question of sig- 

 nificance of these data and criticisms advanced are discussed in Appendix I 

 (p. 729). The respiratory gradient parallels the gradient of methylene 



7 Hyman, i923(j; Child and Hyman, 1926. 



