236 



THE POPULAR SCIENCE MONTHLY. 



of levers moved by muscles ; but in the vertebrates the lever is 

 within and the motor muscles are without, while in insects the 

 muscles are inside and the lever outside. We have already pointed 



out the adaptation of the legs 

 to the habits and the abode of 

 the animals. The hairs with 

 which the tarsi are furnished 

 have a part in permitting flies 

 to move on polished objects 

 and to assist the rapid course 

 of hydrometers, or skippers, 

 on the surface of water. The 

 wings sometimes come into play 

 in propulsion on water ; they 

 are then furnished with long 

 cilia, forming broad oars. The 

 mechanism of flight has been 

 the object of important studies 

 by Pettigrew and Marey. A 

 wasp, the ends of whose wings 

 have been gilded, presents the 

 appearance as shown in Fig. 19. 

 The dispositions of the elytra 

 of the Coleoptera during flight 

 are extremely various. Poujado 

 has given some interesting 

 drawings of them in the annals 

 of the Entomological Society 

 of France. In them the cock- 

 chafer, the Onthopagus, 



is 



Fig. 17. Digestive Apparatus of a Sucking 

 Insect (Ascalaphus meridionalis). a a, an- 

 tennas ; b, salivary glands ; c, oesophagus ; 

 d, stomach ; e, gizzard ; /, chylific ventri- 

 cle ; gff, tubes of Malpighi ; h, intestine ; shown simply raising its elvtra, 



i rectum ; j, last segment of the abdomen. the Necrop J wrus lifting them 

 (After Leon Dufour.) . s ,,,,-, 



in a plane perpendicular to that 

 of the body, and another genus holding them closed as in a posi- 

 tion of rest. Sometimes, also, in moving through the air, the 

 middle legs are raised above the body. 



SVIII svn SVT SV SIV S"' S" S' s 



Fig. 18. Disposition of the Stigmata of a Silk-worm, S, stigmata of the first ring ; S r , 

 stigmata of the fourth ring; S" to SVIII, stigmata 6ituated on the fifth, sixth, and elev- 

 enth rings. 



A considerable number of insects secrete products, some of 

 which are useful, while others are injurious. First in order 



