24 ON THE ORGANS OF HEARING IN INSECTS. 



definitive conclusion respecting the functions of this organ, though it 

 appeared to have a structure analogous to ears. 



I believed I had discovered the organ of hearing in the cockroach, 

 (Blatta orientalis), in the form of an opening, covered by a membrane, 

 white, interiorly concave, and situated at the base of the antennae. 

 Under it there is a projection from the brain (the first nerve knot or 

 ganglion), which appears to perform the office of an auditory nerve. The 

 membrane was not round but semicircular, and immediately bordering 

 on the ring in which the antennae are fixed. Under it I found a white 

 horny substance, similar to that which covers the inner crustaceous 

 envelope of the head. The projections from the brain appeared to give 

 off nerves to the antennas on each side ; but I could not determine 

 whether it spread out over the membrane, which I am inclined 

 to consider the organ of hearing, as I could not otherwise conceive of 

 its functions. 



The antennae of butterflies terminate in a clubbed tip, in which 

 there are not muscles for producing motion, as in the body of these 

 organs, but a half liquid substance filling the cavity. In the alderman 

 butterfly (Ammiralis Atalanta), I found this substance intermixed with 

 membranous matter, resembling in some degree the substance found 

 in the auditory sacs (horsackeii) of the frog, the calcareous portions 

 being less than in the latter. I think it exceedingly probable that 

 these clubs of the antennae are the seat of the sense of hearing. 



I formerly remarked (Biologic, vi. 359), that in the dragon fly, in 

 the space on the forehead between the eyes and the antennae, there is 

 a projection covered with a thin membrane, filled with a whitish fluid, 

 which is probably the organ of hearing. t 



In other winged insects, besides beetles, the interior of the head is 

 large, and destitute of any apparent organ which could serve for the 

 perception of sounds. In the breeze fly (Tabanus bovinus), there is 

 on the upper part of the head, between the two compound eyes, a 

 longish, slender (schmale), horny plate ; and above this on the forehead, 

 a small scutiform projection over a hole, between the inner side of the 

 eye, the brain, and the under envelope of the head, continued below, 

 and covered with a very thin, blackish, multiplicate, and uniformly dry 

 membrane. When the head is opened under water, many air-bubbles 

 escape from this hole. Besides small nerves appeared to me to be 

 given off from the further side of the brain to be distributed to this 

 membrane, though I could not make myself certain of this. Rosenthal 

 observed a similar membrane in the flesh fly (Musca carnaria) ; but in 



