1877.1 123 



himself so tliat the stridor shall impinge on her cavities, which she in 

 turn keeps exposed, by retaining one or the other femur lowered. In 

 the species of Stenohothrus I have examined, the auditory structure in 

 the female proved largest and best suited for examination by the lens 

 or microscope. Cavities similar to those of the Acridiidce may be 

 observed in male Blattina at the hind margin of the metathorax 

 laterally ; and as regards qualification as auditory organs, they in some 

 respects excel similar cavities near the base of the autennpe. 



To supply the requirements of instrumental music, even in con- 

 junction with the phenomena of wing-beating, the prevalence of an 

 organ of hearing in Lepidoptera would scarcely be demonstrable : for 

 the auditory might be supposed to be supplanted by the other senses, 

 as the selective demonstration of love and rivalry may be seen mani- 

 festing itself in other directions : such as the alluring wing dances, or 

 aggregation of the males, or the sedentary display of the female ; 

 which would postulate an adaptation of the visual rather than the 

 auditory faculty. Or, again, the sexual provision of odorous fans 

 would have relation to the sense of smell. But, on the other hand, 

 in seeking for an auditory organ, protective and generally intimative, 

 we have perhaps greater prestige. 



However this may be, the counterpart of the auditory organ of 

 the Acridiidce exists in the JVoctuina. If after having killed an indi- 

 vidual of a large Noctua, and denuded the abdomen of scales and 

 hair, we examine its junction with the thorax, we observe a constriction 

 of the segments that has occurred in the metamorphosis, whereby the 

 first and second abdominal segments of the caterpillar are represented 

 by dorsal arcs indicating a pedicle. In the Noctuina, the organ to 

 which I attribute the function of hearing, is found between these 

 contracted segments and the metathorax, and, projecting postei'iorly, 

 may be said to occupy the transverse section of the first, second, and 

 third dorsal arcs. It is bounded in front by the metathoracic muscles, 

 and encased posteriorly in a saddle-shaped tube, varying in consistency 

 from delicate white membrane {Acronycta psi, Xylophasia poJyodon, 

 Mania typica, &c.) to a hard, yellow, opaque substance, which a needle 

 point chips with difficulty {Catocala niiftit). The external ear {a) is 

 recognised in a largish cavity (meatus), that here penetrates the 

 abdomen at either side, oval in section, with a posterior excavation or 

 conch ; that occasionally extends as far back as the termination of the 

 third segment, conferring on its mouth (in X. polyodon ? ) an extreme 

 length of 2'" and depth of 1'". 



Certain accessories to the cavity are invariably present. One is 

 a minute protuberance posteriorly in the conchoidal excavation; semi- 



