54 ILLINOIS BIOLOGICAL MONOGRAPHS (296 



lated, still expelling water. Often after a few hours they appear normally 

 active, altho seldom feeding until several hours after apparent recovery. 

 The evidences of the regaining of activity take place almost invariably 

 in the above order. 



The stage of activity reached with individuals which faU to recover 

 varies according to the resistance of the species and to the length of time 

 submerged. When kept under water for a time much longer than that 

 required for drowning, sometimes no movement can be produced by 

 stimulation. !More often, however, the earlier stages of activity are passed 

 through, followed by a decline evidenced by a repetition of the same stages 

 in reverse order. Frequently larvae which have apparently thoroly 

 recovered, crawling actively about, refuse to eat and die within two or 

 three days. This indicates that the length of time for which they were 

 submerged is very close to the minimum time required for drowning for the 

 species in question. 



The extent of activity developed before the decline sets in offers a 

 valuable guide to the determination of the minimum time required for 

 drowning, which is the object sought in these experiments, since this factor 

 enables us to express in numbers the resistance to submergence of various 

 species. From the data collected it has been possible in most cases to 

 determine within rather narrow limits the average minimum time required 

 for drowning. When one-half or one-third of the individuals of an experi- 

 ment die and the rest survive, the time for which they were submerged is 

 taken as representing approximately the resistance to submergence for the 

 species. 



Altho different instars of the same species present no uniform difference 

 in resistance, we find some individual variation in this respect, which is 

 most probably to be accounted for by unavoidable physiological differences 

 in the material. Such factors as the time expired since molting, the amount 

 of food in the alimentary canal, and the weather conditions under which the 

 material was reared undoubtedly influence the resistance to submergence 

 to a greater or less extent. The first of these, which will be discussed later, 

 is probably the most important. It is to be regretted that data regarding 

 the resistance of larvae of different broods have not been obtained, since 

 such data would be of considerable interest with respect to those species 

 having several broods a year and hibernating as partly grown larvae. Our 

 experiments with such species have been performed solely with larvae of 

 the hibernating brood after hibernation had been passed. Very probably 

 those of the summer broods are less resistant. If this be true, it would be of 

 great interest to determine whether the difference in resistance in different 

 broods is innate or induced by climatic factors. 



The specific variation in resistance to submergence is extreme, ranging 

 from 25 minutes to 48 hours. The exact nature of the adaptations, mor- 



