i 9 4 



ELEMENTARY ZOOLOGY 



margin of each hind wing against the hind margin of each 

 fore wing when the locust is flying. For hearing the 

 Orthoptera are provided with auditory organs having the 

 character of tympana or vibrating membranes. In the 

 locusts these ears (fig. 51) are situated on the dorsal 

 surface of the first abdominal segment; in the katydids 

 and crickets they are in the tibiae 

 of the fore legs. The food of 

 locusts, crickets, and katydids is 

 vegetable, being usually green 

 leaves ; the cockroaches eat either 

 plant or animal substances fresh 

 or dry, while the praying mantis 

 is predaceous, feeding on other 

 insects which it catches in its 

 strong grasping fore legs. The 

 walking-stick or twig insect is an 

 excellent example of what is called 

 1 ' protective resemblance ' ' among 

 animals. Indeed most of the 

 FIG. 57. A bird louse, Mr- Orthoptera are so colored and 



mus prcest an s, irom a tern, 



Sterna maxima. Most birds patterned as to be almost indistin- 

 w^nglest^bitin'g 11 inlets! guishable when on their usual rest- 

 called bird-lice, which are ing- or feeding-grounds. Some 



external parasites feeding , ., . ^ ,. 



on the feathers of the bird f the tropical Orthoptera carry 

 host. The bird louse to a marvelous degree this modi- 

 figured is about T V in. long. -..''/' 



(Photo-micrograph by Geo. fication for the sake of protection. 

 O. Mitchell.) j n t hi s connection read Chapter 



XXXI referring to ' Protective Resemblances ".) 



Odonata and Ephemerida : the dragon-flies and May- 

 flies. TECHNICAL NOTE. Obtain specimens of adult and imma- 

 ture dragon-flies. The young dragon-flies (fig. 59) may be got by 

 raking out some of the slime and aquatic vegetation from the bottom 

 of a small pond. Compare the external structure of the adult dragon- 

 flies with that of the grasshopper ; note the large eyes, the narrow 

 nerve-veined wings, the biting mouth-parts, and the short antennae. 



