522 



INSECTA 



The separation of the body into the three regions known as head, 

 thorax and abdomen is more distinctly marked in Insects than in 

 any other of the Artlculata. The number of somites and appendages 

 appears to be constant ; the head, with its four pairs of appendages, 

 being composed of four segments, the thorax of three, the abdomen 

 usually of nine or ten (eleven) (OrtJiopiera) (fig. 428). The anterior 

 abdominal segment, however, not (infrequently takes part in the 

 formation of the thorax. 



The head, which is al- 

 most always sharply 

 marked off from the tho- 

 rax, is formed of an unseg- 

 mented capsule, in which 

 different regions may be 

 distinguished. These re- 

 gions have been named, 

 face, forehead, cheeks, 

 throat, skull, etc. alter the 

 parts of the Vertebrate 

 head. The upper side of 

 the head bears the eyes 

 laterally, and the antenna?, 

 while on the under part 

 the three pairs of oral 

 appendages are inserted 

 round the mouth. The 

 anterior appendages, the 

 antenna?, are in Insects 

 formed of a simple row 

 of segments, but vary 



Fio. ISO. Different forms of antemirp (:if;cr Bur- much in form and size. 

 meister). , iJristlc-like antenna of Locust a ; ''. rpi 11 r 



filif orm antenna of Caraitw/c.moniliform antenna ll O' 



of Tcnelrio il, dentate of Eluta- ; e, pectinate 

 antenna of Ctmi<-< m : f, crooked antenna of A/ii.-- ; 

 g, club-shaped of Siljiha ; li, knobbed of -Vtrru- 

 pltorus ; i, lunicllnted of J/t -lolontha ; t, antenna 



the frontal region, and 



with bristle from fi 



serve not only as tactile 

 organs, but also as or- 

 pins of smell. We can 

 distinguish between regular antenna? (where all the joints are alike) 

 and irregular antenna? (fig. 429). The first may be bristle-like, 

 filiform, moniliform, dentate, or pectinate; the irregular antennas, 

 in which the second joint and terminal joints are especially 

 liable to modification, are most frequently club-shaped, knobbed. 



