1877.] 1-5 



lower proceeds, in the direction of the third thoracic ganglion, a 

 silvery nerve (n) (auditory of Miiller and Siebold), running obliquely 

 across and round the elevator muscle of the hind-wing. 



Lastly, by dissevering the abdomen of a Noctua at the junction 

 of the third and fourth segments, and laying bare the posterior, saddle- 

 shaped, transverse encasement of the organs of 'hearing, a judicious 

 use of the needle-point will reveal some accessories to the parts 

 described. It will then become clear, that above the cellular bladder 

 (h) containing the membranous vesicle and nerve, parted by a mem- 

 brane, sometimes white with a shining spot, sometimes wholly iridescent 

 and mirror-like, is a second cavity (c), contained in a more or less 

 ovate process, which on either side forms as it were a pommel of a 

 saddle. This second cell, sometimes parted from the corresponding 

 one by another mirror, wall be found on the one hand to be in connection 

 with the bladder {b) containing the membranous vesicle and nerve by 

 means of a little orifice : and on the other to communicate with the 

 external air by a lateral chitinous tube ((/) that opens at the side of 

 the abdomen at the junction of the third and fourth dorsal arcs (at-E), 

 immediately above the conch of the external ear. This is unmistakeably 

 the counterpart of the Eustachian tube, suitable to balance the atmo- 

 spheric pressure on the delicate membrane of the tympanum. Behind 

 and beneath the entire structure lie the large basal abdominal bladders, 

 developed in Lepidoptera and Diptera. 



Such are the essentials of an organ adapted to hearing in the 

 Noctuina, resembliug the Acridiian structure so closely that the 

 diagram given, would exemplify the usual parts in either. The chief 

 point of departure is the convoluted adjunct of empty cells (J), c, d), 

 with mirror-like partitions, variously developed in Lepidoptera. I 

 have noticed this formation in the Bomlycina and large Geovielrina ; 

 more rudimentary in Crocallis elingunria, it projects on either side into 

 the abdominal air-bladders, in the form of two isolated pear-shaped 

 bodies, partially divided by a septum, and terminated by an iridescent 

 mirror. It may be traced in certain Dz^ifera {Tipula). Goureau, in 

 searching for the musical organ of Aclterontia Atropos, has perchance 

 stumbled on the auditory. He mentions a tvhite muscle, inserted in 

 the borders of a slight cavity covered with smooth transparent mem- 

 brane, on either side of the first abdominal segment (just beneath the 

 insertion of the fan). The Coleoptera should also commonly present 

 an organ of hearing ; the antennae have been indicated as such ; there 

 are also membranes in a horny setting, on the metathorax i)osterioriy 

 at the root of the hind-wings, likelv to reward examination. 



