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 Articulata. 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) (Orthoptera) (fig. 428). The anterior 

 abdominal segment, however, not unfrequently takes part in the 

 formation of the thorax. 



The head, which is al- 

 most always sharply 

 marked oft" from the tho- 

 rax, is formed of an unsesr- 



O 



mented capsule, in which 

 different regions may be 

 distinguished. These re- 

 gions have been named, 

 face, forehead, cheeks, 

 throat, skull, etc. after 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 

 much in form and size. 

 They usually arise from 

 the frontal region, and 

 serve not only as tactile 

 organs, but also as or- 



FIG. 429. Different forms of antennae (after Bur- 

 rueister). a, Bristle-like antenna of Looistu ; I, 

 filiform antenna of Carabug ; c, moniliform antenna 

 of Teuflrio ; d, dentate of Eluter ; e, pectinate 

 antenna of Ctenicera ; f, crooked antenna of Apis 

 g, club-shaped of Silphu ; >i, knobbed of Necro- 

 fihorus ; i, lamellated of Melolonthu ; /.-, antenna 

 with bristle from Sarr/us. 



gans of smell. \Ve can 



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

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

 filiform, momliforni, dentate, or pectinate ; the irregular antenna?, 

 in which the second joint and terminal joints are especially 

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



