336 



GENERAL BIOLOGY 



cells. Although these veins or nervures vary considerably in different 

 species they are quite constant in members of the same species and so 

 are often used as a basis of classification. 



The principal longitudinal veins are the costa ( ), 



subcosta, radius, media, cubitus ( ), and anal. 



There are also cross veins. Any variations are the result of either 

 additional and lessened numbers of those just mentioned. In beetles the 

 fore-wings are sheath-like and called elytra ( ). 



The fore-wings of grasshoppers and all members of orthoptera are 

 leathery and called tegmina ( ). 



The abdomen consists of eleven segments, the posterior one less 

 clearly defined than the others. 



The entire exoskeleton is divided by sutures ( ) 



into distinct pieces, the sclerites ( ), though several 



of these sclerites may fuse. 



Fig. 219. Ear of Locust (Caloptenus italicus) as seen from the inner side. 



T, tympanum ; TR, its border ; o, u, two bone-like processes : bi, pear-shaped 

 vesicle ; n, auditory nerve ; ga, terminal ganglion ; si, stigma, or spiracle ; m, open- 

 ing muscle, and m 1 , closing muscle of same ; M, tensor muscle of tympanic mem- 

 brane. (After Graber). 



The sclerites (Fig. 204, A) on the dorsal surface are called tergites 

 ( ). These are often fused together in various 



insects. The sclerites on the ventral surface are known as sternites 

 ( ), while the side walls connecting dorsal and 



ventral sclerites are called pleurites ( ). 



Should one wish to speak of the entire dorsal portion it is spoken 

 of as the tergum or notum ( ), while the entire ven- 



tral wall is called the sternum and the lateral wall the pleuron. 



The last tergum is sometimes called the suranal ( ) 



