PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS loi 



In regard to data on differential dye reduction in adult hydrozoa, the 

 use of methylene blue with Pelmato hydra oligactis, the common brown 

 hydra, shows reduction progressing basipetally in each tentacle and basip- 

 etally from the hypostome to, or almost to, the more slender stalk. In 

 unattached animals the foot usually reduces earlier than the stalk, and re- 

 duction progresses acropetally over more or less of the stalk. In attached 

 animals or advanced buds attached to the parent the stalk usually reduces 

 later than the body proper. Motor activity, local contractions of body or 

 stalk, may alter the reduction gradients to a considerable degree. In un- 

 attached animals the stalk is usually more or less motile, contracting and 

 extending frequently, and reduces more rapidly than when inactive. When 

 an animal bends strongly to one side while reduction is proceeding, the 

 color may disappear completely from the contracted side and reappear 

 when relaxation occurs. This local reduction accompanying or following 

 contraction, with reoxidation of the dye on relaxation, has been observed 

 repeatedly. 



Methylene blue reduction progresses basipetally in each tentacle of 

 Corymorpha and in the hydranth body if not altered by contraction. That 

 oxygen uptake of the hydranth is relatively great is indicated by occur- 

 rence of dye reduction in open solutions of dye in the hydranth body and 

 the proximal regions of the crowded tentacles if the hydranth is left with- 

 out change of position for even a few moments. Frequent change of posi- 

 tion or increase of oxygen about the hydranth by agitation of the medium 

 brings about reoxidation. The dependence of hydranth reconstitution on 

 oxygen tension in the related genus, Tuhularia, indicates similar condi- 

 tions as regards oxygen uptake of the hydranth (Barth, 1938^). Reduc- 

 tion also progresses basipetally in the ectoderm of the naked Corymorpha 

 stem, except for a slight increase in rate of reduction in the extreme prox- 

 imal region. From the basal region of the stem, inclosed in perisarc, nu- 

 merous holdfast stolons arise as buds and elongate with growing region at 

 the free end; in each of these rate of reduction decreases from the tip basip- 

 etally (Child and Watanabe, 19356). In isolated pieces of the Cory- 

 morpha stem, rate of reduction adjoining a cut end is increased following 

 section, and a gradient of decreasing rate extends from the cut end for a 

 greater or less distance. The region from which the hydranth will develop 

 later is the high region of this gradient, and within a few hours after sec- 

 tion the length of the hydranth primordium is indicated by a well-defined 

 region at one or both ends of the piece, where reduction is more rapid than 



