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Annals Entomological Society of America [Vol. VI, 



alimentary canal of adults taken in the field, has confirmed 

 this. Water seems much more essential than food for these 

 adults. If ever found out of hiding in their cages, they were 

 almost sure to be on the stones in the pans with their mouths 

 buried in water. Entirely deprived of water, ' the average 

 length of life is shortened by several days. 



Fig. 1. 



Fig. 2. 



Fig. 1. 



a. Left mandible of the nymph, inner surface. 



b. Left mandible of the adult, same view and magnification. 



Fig. 2. 



a. Abdomen of the female, ventral view showing the modification of the eighth 

 sternite. 



b. Abdomen of the male, dorsal view showing the genital armature with the 

 penis extruded. 



Both figures drawn -to the same scale. 



The voraciousness of the nymphs is necessary, since the 

 adults abstain from food and since enough energy must be 

 stored up to last through aerial life and the completion of the 

 final function, reproduction. 



Mating. Ordinarily mating begins soon after emergence. 

 The readiness with which it takes place in captivity has been a 

 great surprise on account of the natural timidity of stone-flies. 

 Frequently pairs have been found in copula in the breeding 

 cages and have been removed to adult quarters without arousing 

 enough alarm to cause their separation. By careful manipu- 

 lation copulating pairs can even be held in the palm of the 

 hand. This has made a detailed study of mating possible. 



