EXTERNAL ANATOMY OT INSECTS. 51.5 



the body of the insect a ; while in Ma?itis, Acrida K. and 

 Psocus, they are as slender as a hair. The antennas in 

 many of the Prio?ii, especially in P. imbricornis, are thick 

 from base to tip ; while in other Capricorn-beetles they 

 are quite the reverse. 



It will not be necessary to enlarge here upon the ge- 

 neral form of these organs : I shall therefore only notice 

 the two principal divisions of them in this respect. — 

 Antennas, regard being had to one of their uses, may be 

 divided into two sections, distinguished by forms ex- 

 tremely different: those, namely, that are employed by 

 insects as factors to explore their way, and those that 

 cannot be so employed. The great majority are of the 

 former kind ; but those that may be denominated setige- 

 rous, — as the antennas of the Libellulina, Ephemerina, of 

 the Homopterous Hemiptera, and of many Diptera, the 

 last joint of which terminates in a bristle, or is furnished 

 with a lateral one, and of some gnats that have short 

 feathered antennas, — appear not fitted to be used as tac- 

 tors to explore by touch, and form the latter description. 

 This difference in these organs, as I shall have occasion 

 to prove more at large hereafter, furnishes a strong pre- 

 sumption that their primary function is not touch. Were 

 this the case, it would be common to them all. 



As to their structure, antennas consist in general of a 

 number of tubular joints ; each of which having separate 

 motion, the animal is thereby enabled to give them every 

 flexure necessary for its purposes. The scape, or first 

 joint, by means of the bulb inosculates in the torulus, or 

 is suspended to it; and the others, sometimes by a simi- 



a Plates XII. Fig. 2&; and XXV. Fig. 9, 24. 

 2 L 2 



