PHYSIOLOGICAL SENESCENCE IN HYDROMEDUSyE. 6 1 



1/15000 after 24 hours, the animals live for several days with all 

 cellular tissues stained. After 48 hours pulsation rate A = % 

 pulsation rate B approximately, where A and B are animals of 

 18-20 and 50-60 mm. respectively. 



Phialidium gregarium. 



The youngest animals found were mostly 7-8 mm. in diameter, 

 while the old, sexually mature individuals measured 20-25 mm. 

 Only a few series of susceptibility experiments were made with 

 this species, HC1 m/i^oo, m/iooo, m/Soo, m/6oo, neutral red and 

 methylene blue being used. The susceptibility relations are 

 similar to those observed in the other species. In this rather 

 delicate form shrinkage is a characteristic feature of the action 

 of various agents, the younger animals undergoing shrinkage 

 earlier and to a greater degree than the old, a decrease of half or 

 three fourths in diameter occurring in many cases. 



Sarsia rosaria. 



In this species the umbrella is very deep, the oral-aboral axis 

 being almost or quite twice the diameter. Depth is therefore a 

 more convenient measure of size than diameter and is commonly 

 used. The sexually mature animals average about 15 mm. in 

 depth of umbrella, but the extremes range from 10-12 mm. on 

 the one hand to 20 mm. on the other. In the smallest and young- 

 est animals found, 6-7 mm. in depth, the gonads had already 

 begun to develop, and although the susceptibility of these forms 

 is characteristically greater than that of the mature individuals 

 the differences in age and in susceptibility in the animals available 

 are not as great as in the other species examined. 



In general, results with this species are similar to those with 

 others but in some pairs an individual 12-15 mm. showed a sus- 

 ceptibility equal to or even greater than that of 7-8 mm. animals. 

 Since none of the animals within these limits of si/e represent 

 very great differences in physiological age, all being near sexual 

 maturity, it is to be expected that occasionally a larger animal 

 will show a higher susceptibility than a smaller. 



The agents used were KNC 777/50000, m/ioooo, m/^ooo, HC1 

 m/iooo, m/6oo, m/^oo, m/^oo, neutral red and methylene blue, 



