140 



C. M. CHILD. 



In the higher concentrations a slight basipetal color gradient 

 appears, but he r e again the posterior end commonly also stains 

 almost as rapidly as the anterior, suggesting the existence of a 

 secondary region of high activity there. Earlier work with 

 susceptibility agents indicated a slight basipetal gradient in the 

 majority of individuals, but the results were not as uniform as in 

 many other species (Child, '14). It seems at least possible that 

 certain irregularities in disintegration observed in the earlier 

 work depend in part on the existence of a second region of rather 

 high susceptibility in the posterior part of the body. 



Five genera of hydromedusae, Phialidium, ^Equorea, Mitro- 

 coma, Sarsia and one undetermined genus, tested repeatedly in 

 permanganate, have shown in all cases a more rapid staining of 

 the ectoderm of the subumbrella, than of the exumbrella. The 

 difference is apparently greater in young than in old animals. 

 These results agree with those of McClendon ('18) on oxygen 

 consumption in the scyphomedusa Cassiopea xamachana. He 

 found that the oxygen consumption of the subumbrella, exclusive 

 of the manubrium is more than four times that of the exumbrella 

 in the resting animal, with a still greater difference when pulsa- 

 tions occur. Each medusa tentacle also shows a basipetal color 

 gradient. 



In the colonial hydroids, Bougainvillea, Obelia, Gonothyria 

 and one undetermined campanularian genus each hydranth 

 body and each tentacle shows a basipetal color gradient, and 

 with low concentrations a colony gradient also appears, i. e., in a 

 long stem with primary, secondary and perhaps tertiary branches 

 the hydranths and growing tips of the apical region of the whole 

 colony stain more rapidly than those of the basal region and the 

 same differences appear on each of the longer primary branches. 

 This colony gradient is clearly visible to the naked eye when the 

 whole stem with its hydranths is placed in water after staining. 



A basipetal color gradient also appears in the stems of the 

 colony, the growing tips always staining much more rapidly and 

 deeply than more basal regions. As regards these stems, however 

 there is of course the possibility that the permanganate may pene- 

 trate the thinner perisarc of apical growing regions more readily 

 than the thick perisarc of more basal levels, though, as a matter 



