THE PERIODICAL CICADA 



ages, but those of the legs are usually inverted during 

 the shedding and disappear from the outside of the slough, 

 though the holes where they were pulled in can be found 

 before the membrane becomes too dry. 



The nymph (Figs. 125, 7; 126) usually runs about at 

 first in the groove of the twig containing its egg nest and 

 then goes out on the smooth bark. Here any current 

 of air is likely to carry it off immediately, but many 

 wander about for some time, usually going toward the 

 tips of the twigs, some even getting clear out on the leaves. 

 But only a few nymphs are ever to be found on twigs 

 where piles of embryonic skins show that hundreds have 

 recently hatched; so it is evident that the great majority 

 either fall off or are blown away very shortly after emerg- 

 ing. Many undoubtedly fall before the shedding of the 

 egg membrane, for the inclosed creature has no possible 

 way of holding on, and even the free nymph has but feeble 

 clinging powers. Those observed on twigs kept indoors 

 often fell helplessly from the smooth bark while appar- 

 ently making real efforts to retain their grasp. Their 

 weak claws could get no grip on the hard surface. In- 

 stead, then, of deliberately launching themselves into 

 space in response to some mysterious call from below, 

 the young cicadas simply fall from their birthplace by 

 mere inability to hold on. But the same end is gained — 

 they reach the ground, which is all that matters. Nature 

 is ever careless of the means, so long as the object is at- 

 tained. Some acts of unreasoning creatures are assured 

 by bestowing an instinct, others are forced by with- 

 holding the means of acting otherwise. 



The cicada nymphs are at first attracted by the light. 

 Those allowed to hatch on a table in a room will leave 

 the twigs and head straight for the windows ten feet 

 away. This instinct under natural conditions serves to 

 entice the young insects toward the outer parts of the 

 tree, where they have the best chance of a clear drop 

 to earth; but even so, adverse breezes, irregularity of the 



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