loo FIRST LESSONS IN ZOOLOGY 



with a string- fastened to the middle of the bottom. There 

 are other species of cicadas besides the seventeen -year-old 

 kind, with shorter hves, a common one being the farnihar 

 harvest-fly or dog-day locust, which requires only two 



Fig, 137.— Tite scventet'ii-vciLr cic^nhi, L'u^uid sc/'/iinh'i-iin; the specimen at 

 left showiiiL,^ sound-making <.'rgan; v,p, ventral plate; t^ t\'mpaniim. 

 (From specimens.) 



years for its development. This is large, and black and 

 green in color, while the seventeen-year cicada is smaller, 

 and black and reddish-brown. 



Other insects conspicuous for the sounds they make are 

 the katydids and crickets. The loud sounds of insects 

 are not made by a "voice " that is, by vocal cords set 

 into vibration by the breath. In the katydids and crickets 

 the familiar shrill sounds are made by rubbing together 

 the bases of the front A\'ings, which are specially modified 

 for this purpose. The veins are thickened and rough- 

 ened by little transverse ridges forming a sort of scraper 

 or rasp, so that the membranes are set into strong 

 vibration when the base of one wing is scraped or rubbed 

 over the base of the other. Only the males are provided 

 with these musical organs. 



There are about a dozen species of tree and bush katy- 



