STRUCTURES USED IN CLASSIFICATION. 



17 



This may be high or low, crested, arched, distinct, aborted, 

 etc. It is usually cut by one or more notches formed by shallow 

 grooves or sulci which cross the disk of the pro- 

 notum and extend down its sides. The hindmost 

 of these sulci or grooves divides the disk of the 

 pronotum into two parts known as the prozona 

 (/>.?) and iii<'t(i.:-<>n<t im.c). The fore and hind 

 margins of the disk of pronotum may be truncate, 

 rounded, angled, notched, etc. The surface of the 

 disk is usually smooth, but sometimes wrinkled 

 and may be rugose or roughened with numerous 

 tubercles. 



Fig. (>. Dorsal 



view of head and 

 pronotum. (After 



The under or ventral side of the prothorax is 

 a narrow, somewhat movable piece called the prosternum. On 

 its center it often bears a tooth or spine (]>i'o. */>. ), the presence 

 or absence and shape of which form characters used in classifica- 

 tion. Near the outer ends of the prosternum are shallow sockets 

 in which are attached the front pair of legs. 



The )iicftotJioi'a.r and ni<'tailioi'<t-i\ the second and third seg- 

 ments of the thorax, are, in the locust, rather firmly united with 

 the basal abdominal segment of the abdomen to form a firm 

 walled box, though in the Blattidae they are distinct. The upper 



portion of these segments is, in 

 most Orthoptera, partly or 

 wholly covered by the pronotum 

 or base of the outer wings. To 

 the mesothorax are attached the 

 tegmina or outer pair of wings 

 and the second or middle pair 

 of legs. To the meta thorax are 

 joined the inner wings and the 

 third or hind pair of legs. The 

 under or ventral portion of 

 these segments are called re- 

 spectively the mesosternum and 

 111 eta sternum. (Fig. 7.) The 

 former in the locust is com- 



Fig. 7. Lower or ventral view of the 



thorax of a locust. (After Lugger.) posed of a front transverse por- 



tion, with two nearly rectangular lobes projecting backward. Be- 

 tween these lobes is dove-tailed a squarish tongue, or forward 

 prolongation of the metasternum. The latter is united with the 



