58 C. M. CHILD. 



after 2-3 minutes in both old and young, often slightly earlier 

 in the young. After one hour in HC1 pulsation reappears after 

 10 minutes in the old, and after 12-13 minutes in the young and 

 after 2^2 hours in HC1 pulsation reappears in the old after 25, 

 in the }^oung after 45 minutes. The longer the exposure the 

 more the young animal falls behind the old in recovery. After 

 20 minutes in HC1 772/400 young animals 18-20 mm. did not re- 

 cover at all while old animals 60 mm. showed slight pulsation 

 after four hours in water. Recovery after KNC is much slower 

 and occurs only in much lower concentrations. 



In all concentrations of KOH from m/iooo to about 772/250 a 

 primary acceleration of pulsation rate and increase in strength 

 of contraction occurs, but in concentrations higher than 772/250 

 pulsation usually ceases at once or in a few seconds. During 

 this primary acceleration the pulsation rate is often doubled, but 

 since the maximum rate usually persists only a few seconds and 

 is followed by progressive decrease in rate it is difficult to deter- 

 mine whether the degree of primary acceleration differs in a char- 

 acteristic way with age. It is certain, however, that the retarda- 

 tion following the acceleration occurs more rapidly in young than 

 in old animals, so that pulsation ceases first in the young, as 

 Table IV. indicates. 



The opposite primary effects of acid and alkali on the pulsation 

 rate are what might be expected in the light of what we know of 

 their action on living protoplasm in general. In lethal concen- 

 trations, however, their action, following the primary effect, is 

 essentially similar and the relations between susceptibility and 

 age are the same for both. 



Mitrocoma discoidea. 



In this species the jelly is much less firm than in JEquorea, and 

 marked shrinkage occurs in the young animals in acids and some 

 other agents. Muscular contraction as distinguished from pulsa- 

 tion is much more frequent even in nature than in sEquorea. 

 Frequently contraction brings about a folding of the umbrella 

 with the two halves of the margin approximated or apposed along 

 a straight line, or the margin may become square or very irregular 

 in outline. The contracted condition may persist for several 



