INSECTA. 369 



prothorax and head ; but the infundibuliform trachea sends off no 

 branches in its course through the prothorax. Pursuing this tracliea 

 from the infundibuhxr beginning backwards to the coxa of tlie an- 

 terior feet, we see that here it sends off various lai'ger and smaller 

 branches, but enters the limb without material diminution of calibre. 

 In traversing the slender knee, the trachea is obliged to contract ; 

 but it soon again expands, and forms at the part of the tibia of the 

 lirst pair of legs, where the two folds and apertures are seen, a long 

 vesicular dilatation of a peculiar form. This vesicle is in con- 

 nection, externally, with a tympanic membrane closing an orifice in 

 the leg, and internally with a peculiar part of the nervous system. 

 Two nerves, both derived from the first thoracic ganglion, and 

 both unusually large, accompany the trachea down the leg : the lesser 

 nerve attaches itself to the vesicular dilatation, and there expands 

 into a flattened ganglion, on which is situated a row of transparent 

 vesicles containing a collection of cuneiform, staff-like bodies, with 

 very finely pointed extremities, Avhich are surrounded by ganglion- 

 cells. An undulated prolongation of the ganglion is thence con- 

 tinued, and is lodged in a depression on one side of the vesicle. The 

 aperture in the leg is compared to an external ear ; the membrane 

 closing it and the chamber behind, to the tympanic cavity and drum ; 

 the nerve and ganglion to the acoustic nerve ; and the thoracic aper- 

 ture to the Eustachian tube. It is strange, however, that the organ 

 under so well marked a form should not exist in the tree-hoppers 

 (^Cicadce), which attract their females by peculiar notes. In these 

 Homoptera the soft capsular membrane of the joint of the antenna, 

 which in some movements may be rendered tense, has been alluded 

 to by Burmeister as a structural indication of the organ of hearing 

 in the peculiar appendages in which he supposes, with many other 

 entomologists, that the sense resides. Two, at least, and often more 

 numerous, nervous filaments from a slight ganglionic enlargement 

 penetrate the antenna3 in insects ; and these may subserve the distinct 

 offices of the appreciation of the vibrations of sound, of the characters 

 of surface, and of the regulation of the movements of the antennsB. 



Of all the organs of the special senses not only is that of sight 

 manifest without ambiguity, but it is more complicated and relatively 

 larger in insects than in any other class of animals. 



"What would be thought of a quadruped, whose head, with the ex- 

 ception of the mouth and the place of juncture with the neck, was 

 covered by two enormous convex masses of eyes, numbering upwards 

 of 12,000 in each mass ? Yet such is the condition of the organs of 

 vi.-jjon in the dragon-fly, which, besides the two great compound eyes, 



B n 



