92 C. M. CHILD. 



decreasing basipetally. Elongated manubria show similar gradi- 

 ents in rate of reduction. Manubrium and margin are regions 

 of more rapid reduction than other subumbrellar regions, but the 

 subumbrellar ectoderm in general reduces more rapidly than the 

 exumbrellar ectoderm. Dehydration and clearing is not neces- 

 sary in the medusa species used because the cellular tissues are 

 mostly in such thin layers that they do not become opaque black. 

 Nevertheless, the final difference in depth of color between 

 exumbrella and subumbrella cannot be regarded as a fair criterion 

 of differences in total amount of reduction because the thickness 

 of cellular tissue is much greater in the subumbrella than in the 

 exumbrella. On this account I am inclined to regard the differ- 

 ences in rate of reduction as more significant than the final 

 differences in depth of color. The jelly reduces little perman- 

 ganate and reduction is very slow. 



Data on susceptibility of medusae have not previously been 

 recorded, but numerous experiments have been performed, 

 chiefly on ^Equorea, but in part on other species, with various 

 concentrations of several agents, viz., KNC, m/ioo-m/$oo, 

 HC1, m/2oo-m/8oo and KOH, m/2oo-m/6oo. The susceptibility 

 gradients in all these agents are essentially the same as the reduc- 

 tion gradients. A few experiments with neutral red and methy- 

 lene blue and various other agents on the smaller forms gave 

 similar results. It may be said then that here, as in the hydroids, 

 the susceptibility gradients and the reduction gradients corre- 

 spond. 



It is of interest to note that the higher susceptibility and more 

 rapid reduction of the subumbrellar as compared with the exum- 

 brellar regions is in accord with McClendon's data on oxygen 

 consumption in Cassiopea. He found that the subumbrella 

 consumed much more oxygen per unit of weight than the ex- 

 umbrella plus the greater part of the mesoglcea (McClendon, '17). 

 Dr. Bellamy and Dr. Hyman have found differences in electric 

 potential corresponding to the differences in susceptibility and 

 rate of reduction, not only as regards subumbrella and exum- 

 brella, but also as regards marginal and oral, as compared with 

 other subumbrellar regions. The regions of highest galvano- 



