526 



ES'SECTA. 



while on the mesonotum there is a median triangular- plate (the 

 scutelhtm), and on the rnetanotum there is not rarely a similar but 

 smaller shield (the postscutettum). The manner in which the three 

 regions of the thorax are connected with one another varies in the 

 different orders. In the Coleoptera, Neuroptera, Orthoptera and in 

 many Rhynchota, the pro-thorax is freely movable, wliile in all other 

 cases it is a relatively small ring and is fused with the following 

 segments. 



The three pairs of legs are articulated in excavations of the 

 chitinous integument of the ventral surface between the sterna 

 and pleura. The number and size of the joints of the legs seem 



FIG. 435. Different form of legs (r&gno animal), a. Mantis with predatory leg ; 6, leg of 

 Caralus used in running; e, of Acridinm used in springing; d, of Gryllotalpa used 

 in digging; e, swimming leg of Dytiscus. 



more constant in the Insecta than in any other group of the Arth- 

 ropoda, so that it is possible to distinguish five regions (fig. 435). 

 The basal joint (coxa), which is either spherical or cylindrical, is 

 articulated to the thorax and permits of free movement of the limb. 

 The coxa is followed by a second very short ring, constituting the 

 trockttnter, which is sometimes divided into two parts or in other 

 cases is fused with the next joint. The third joint, which is con- 

 spicuous on account of its size and strength, is the long femur. The 

 next joint is the likewise long but slender tibia, which is armed at 



