414 PATTERNS AND PROBLEMS OF DEVELOPMENT 



or lo per cent CO2 all hydranths developed at the proximal ends. With 

 short pieces results are similar but "less striking." With the same oxygen 

 tension at both ends circulation of water at one end determined hydranth 

 development there (J. A. Miller, 1937, 1939). Corymorpha resembles 

 Tubularia as regards susceptibility to low oxygen. The hydranths soon 

 die in standing water. When individuals in good condition are stained 

 with methylene blue and placed in standing water, oxygen tension soon 

 becomes so low about the basal regions of the crowded tentacles and 

 about the manubrium that the dye is rapidly reduced there in well- 

 aerated sea water with large surface open to air. In rapidly flowing water 

 the dye is not reduced. Various attempts have been made to subject the 

 two ends of Corymorpha pieces to different oxygen tensions; but by means 

 of contraction, extension, and changes in diameter the naked stems usually 

 make their way out of the opening in the partition between the two sea 

 waters, or, if the opening fits tightly about the stem, separation usually 

 results. However, other experiments with this species make it highly 

 probable that an oxygen differential can determine which of two polarities 

 shall develop or can actually determine polarity. 



Corymorpha pieces only a few millimeters long show relatively little 

 motility during the earlier stages of reconstitution. Such pieces lying un- 

 disturbed on the bottom of a container are freely exposed to water on 

 one end or side, while the other is more or less closely in contact with the 

 underlying surface and diffusion is more or less interfered with there. 

 That this is the case as regards oxygen is readily shown by the rapid dye 

 reduction on the surface in contact of pieces stained with methylene blue 

 or Janus green and a gradient of decreasing rate of reduction from the 

 surface in contact toward the free surface. 



In 73 per cent of two hundred Corymorpha pieces 5-10 mm. long, sup- 

 ported on thin gauze or loose absorbent cotton near the surface of the 

 water and lying on their sides so that both ends were equally exposed, 

 hydranths developed on both ends. Of a like number of pieces 5 mm. 

 long with one end, either distal or proximal, in contact with the bottom 

 of the container, 30 per cent developed hydranths at both ends, and most 

 of these were pieces that fell over one side in consequence of contractions 

 and extensions. In another experiment hydranths developed at both ends 

 in 66 per cent of fifty similar pieces frequently moved about and turned 

 over by water currents and reversed individually. A similar lot undis- 

 turbed with one end in contact gave 22 per cent bipolar hydranths, most 



