INSECTS : THEIB EABS AMD EYES. 159 



govern their instincts and actions. Among such we may 

 mention, conjecturaUy, the comparative moisture or dry- 

 ness of the atmosphere, delicate changes in its tempera- 

 ture, in its density, the presence of gaseous exhalations, 

 the proximity of solid bodies indicated by subtle vibrations 

 of the air, the height above the earth at which flight is 

 performed, measured barometrically, the various electrical 

 conditions of the atmosphere; and perhaps many other 

 physical qualities which cannot be classed under sight, 

 sound, smell, taste, or touch, and which may be alto- 

 gether imperceptible, and therefore altogether incon- 

 ceivable, by us. It is probable, however, that the 

 antenna are the organs in which the sense of hearing is 

 specially seated ; a conclusion which has long been 

 conjecturaUy held, and which is confirmed by some obser- 

 vations recently made on the analogous organs in the 

 Crustacea, which I will allude to more particularly pre- 

 sently. 



The forms which are assumed by the antenna of Insects 

 are very various ; and I can bring before you only a very 

 small selection out of the mass. One of the most simple 

 forms is that found in many Beetles, as in this Carabus, 

 for example. Here, each antenna is composed of eleven 

 joints, almost exactly alike and symmetrical, each joint a 

 horny body of apparently a long-oval shape, polished on 

 the surface, but not smooth, because covered with minute 

 depressed lines, and clothed with shaggy hair. There is, 

 however, a slight illusion in the appearance : it seems as 

 if the dividing point of the joints were, as I have just 

 said, at the termination of the oval, but when we look 

 closely we see that the summit of eaeh oval is, as it were, 

 cut off by a line, and by comparing the basal joints with 

 the others, we see that this line is the real division, that 

 the summit of the oval really forms the bottom of the 

 succeeding joint, and that the constricted part is no 

 articulation at all. The first, or basal joint (called the 



