258 INSECT ARTIZANS AND THEIR WORK 



noises set up at sunset by birds and monkeys, the 

 latter naturalist says : " Added to these noises 

 were the songs of strange Cicadas, one large kind 

 perched high on the trees around our little haven, 

 setting up a most piercing chirp ; it began with 

 the usual harsh jarring tone of its tribe, but this 

 gradually and rapidly became shriller, until it 

 ended in a long and loud note resembling the 

 steam-whistle of a locomotive engine. Half a dozen 

 of these wonderful performers made a considerable 

 item in the evening concert. I had heard the same 

 species before at Para, but it was there very un- 

 common." 



Concerning the American species known as the 

 Seventeen-year Locust (Cicada seftemdecim), there 

 is an extraordinary feature in its life-history which, 

 though it has nothing to do with its character as a 

 musician, we feel justified in mentioning. It is 

 widely spread over the greater part of the United 

 States, but in any given locality it only makes its 

 appearance in considerable numbers once in seven- 

 teen years. Kalm was the first to call attention 

 to this fact, but his statement appears at first to 

 have been regarded with doubt ; subsequent 

 investigations, however, established the fact, and 

 reasons were sought for the periodicity. 



It is now shown that the insect takes nearly 

 seventeen years — in some States, when the seasons 

 are more uniformly favourable, thirteen years — in 

 its progress from the egg to the acquisition of 

 expanded wings. During this long period, which 



