20 



ELEMENTARY ENTOMOLOGY 



We have stated that the structure of insects often determines 

 the method of treating them. This may now be understood, for 



it is evident that 



/ a poison such as 



Paris green, ap- 

 plied to the food 

 of a sucking in- 

 sect, such as a 

 plant-louse, would 

 not be taken into 

 the mouth through 

 the sucking mouth- 

 parts, which ex- 

 tract only the juices 

 beneath the sur- 

 face, while it might 

 be entirely effect- 

 ive against an 

 insect with biting 

 mouth-parts, which 

 consumed the sur- 

 face covered by the 

 poison. A better 

 understanding of 

 these simple facts 

 of insect anatomy 

 would save Amer- 

 ican farmers thou- 

 sands of dollars 

 every year, now lost 

 through ignorance. 

 Thorax. The thorax is the middle region of the body, composed 

 of the three segments back of the head, which are called the /;-<?- 

 thorax, mesothorax, and metatJiorax respectively. As previously 

 indicated, the differentiation of the thorax has been incidental to 

 the development of the wings, and the structure of the thorax is 

 determined by the development and use of the organs of locomo- 

 tion. A pair of jointed legs is attached to each segment and 



f ' .* j." .-" \ 7 



,///V" .-" --\---h 



B 



D 



FIG. 22. Mouth-parts of an ant (Myrmica rubra) 



A, seen from the lower side in situ; B and D, maxillae; 

 C, labium seen from the upper side, detached ; a, mandible ; 

 t>, maxilla ; c , mentum ; rf, maxillary palp ; e, labial palp ; f, 

 glossa or tongue ; g, adductor muscle of mandible ; //, abductor 

 muscle of mandible ; /, labium ; k, gustatory organs ; /, duct 

 of salivary glands ; ;, maxillary comb ; n, gular apodeme. 

 (After Janet, from Wheeler) 



