192 



SYSTEMATIC ZOOLOGY 



CLASS III. HEXAPODA OR INSECTA 



The Hexapoda (Gr. e'|, six, and 7rot>?, foot), or Insecta (Lat. 

 insecttim, cut up), comprise almost as many species as all the 

 other groups of animals taken together. They vary in size 

 from microscopic individuals to the huge butterflies and moths 

 and beetles, and are of universal distribution. The air is the 

 natural habitat of most insects ; but some live on the ground, a 

 few are parasites, and a few live on the surface of the water, 



fresh or salt, while the 

 larvae of insects, in addi- 

 tion to these habitats, 

 may live in the earth or 

 under water. But, not- 



withstanding 



this great 



size and 



there is a 



Fig. 189. Melolontha vulgaris, a cockchafer. Male, 

 seen from above and slightly enlarged. 1, head, 

 stretched forward ; 2, prothorax ; 3, mesothorax ; 

 4, metathorax ; 5, abdomen; 6, anterior wing, ely- 

 tron, of right side, turned forward ; 7, posterior 

 wing of right side expanded; 8, maxillary palps; 

 9, femur of third right leg; 10, tibia of same; 11, tar- 

 sus of same. (After Vogt and Yung, from Shipley 

 and MacBride's Zoology.) 



diversity in 

 mode of life 

 remarkable uniformity in 

 the characteristics which 

 distinguish this class. 



The body is clearly 

 divided into three re- 

 gions, the head, thorax, 

 and abdomen (Fig. 189). 

 The head is unseg- 

 mented, but consists of 

 at least four fused seg- 

 ments ; it is provided with a firm chitinous covering and usually 

 bears a pair of large compound eyes, often with simple eyes in 

 addition, and four pairs of appendages ; these consist of the 

 many-jointed antennae, and three pairs of mouth parts, which 

 bear the same names as the corresponding organs in the Myria- 

 poda, — mandibles, first maxillae, and second maxillae (Fig. 190). 

 There is very great variation in form in these mouth parts, as 

 they perform such a great diversity of functions in different 

 insects, such as biting, gnawing, piercing, and sucking. 



The thorax is always composed of three separate segments, 

 called the prothorax, mesothorax, and metathorax, and each - 

 ment bears a pair of uniramous, jointed appendages on its ventral 



