IXTRODUCTION. 



lateral and sometimes the central carina are absent. Occasionally 

 the central carina is raised into a ridge, or humped, and spines 

 project from the front angles, or from the sides. On the upper 

 surface of the pronotum we frequently meet with three or four 

 transverse depressions or gi'ooves, the position and extent of 



Fig. •'). — Side view of the pronotum of Criotcitix : a, pronotum, /), tegmen, 

 c, costa of wing. 



which is of some importance in classification ; as is also the shape 

 of the deflexed lobes on the sides of the pronotum. [When there 

 is a central carina it is sometimes complete, sometimes it is cut 

 by one of the transverse grooves, and in some cases by two of the 

 grooves]. 



Behind the pronotum we find the mesonotum and metanotum, 

 followed by the nine segments of the abdomen. The first segment 



Fig. 7. — Side view of pronotum of: (A) Gat^trimarcpm. with central carina 

 cut by one groove ; (B) Bryudema, cut by two grooves. 



bears a curious structure on each side which is regarded as an 

 organ of hearing. [It consists of a cavity covered by a transparent 

 membrane, filled with liquid, and is connected with a nerve 



Fiij. 8.- 



-Side view of the base of tlie abdomen of Schisioccrca, 

 showing: o, the auditory organ. 



originating in the third thoracic ganglion.] Each segment, 

 except the ninth, is provided with a spiracle on each side. There 



