3 I 8 LOCUSTIDAE 



circular space o" is not part of the actual structure, but repre- 

 sents the area of the external acoustic orifice of the prothorax ; 

 it is not, however, so large as it should be. 



Although the tibial ears of Locustidae are very perfect organs, 

 there is great difficulty in deciding on the exact nature of their 

 functions. They would appear to be admirably adapted to 

 determine the precise locality from which a sound proceeds, 

 especially in those cases and they are the highest forms in 

 which the tympanum is placed in a cavity the external orifice 

 of which is a slit (Fig. 193, B) ; for the legs can be moved in 

 the freest manner in every direction, so as to bring the drum 

 into the most direct line of the vibrations. But as to what 

 kinds of vibrations may be perceived, and the manner in which 

 they may be transmitted to the nerves, there is but little 

 evidence. On reference to the diagram it will be noticed that 1 

 the tympanum, the tympanal vesicles, and the nervous apparatus 

 are not in close connexion, so that even the mode by which the 

 impulses are transmitted is obscure. 



The musical organs of the Locustidae are different from those 

 of the Acridiidae, and are invariably situate on the basal part of 

 the tegmina. They are found, in the great majority of cases, only 

 in the male ; in the tribes Ephippigerides and Callimenides they 

 exist in each sex. One of the wings bears a file on its inner sur- 

 face, while the other on the right side of the body is provided 

 with a sharp edge placed on a prominent part of its inner margin. 

 By slightly tilting the tegmina and vibrating them rapidly, the edge 

 passes under the file, and a musical sound is produced. These 

 structures are limited to the small anal area of the wing, and when 

 the tegmina are very greatly reduced in size, it is this part that 

 still remains. There is much variety in the details of the structure. 

 The nervures of this part of the tegmina are different in the 

 male from what they are in the female, and, moreover, the two 

 wing-covers of the male differ from one another. It is apparently 

 the vibrations of the right tegmen that produce the sound, and 

 this part usually bears a space of a glassy nature, which probably 

 improves the character of the sound produced. Our chief British 

 songster of this group, Locusta mridissima, is only provided witli 

 phonetic organs (Fig. 195) of a somewhat imperfect character, 

 but in the genus Mecopoda there is great perfection of the 

 structures. The anal areas of the two tegmina are in this case 



