18 THE ANTENNA. 



rially lightened, as in this the characters derived from 

 the structure of the mouth are of the highest import- 

 ance. We have still, however, a little dry ground to 

 plod over together, and I can only hope that we shall 

 not tire by the way. 



It has already been stated, that besides the organs 

 of the mouth, the head bears the eyes, and a pair of 

 jointed antennae. The description of the structure of 

 the eyes may be left until we come to the consideration 

 of the senses of insects; but a few words may be 

 devoted here to the general structure of the antennae. 

 These appendages usually spring from the front of the 

 head between the eyes, or from its sides immediately 

 in front of those organs. In their most common 

 form they are thread-like organs, composed of a very 

 variable number of joints, sometimes tapering from 

 the base to the tip, and sometimes in the opposite 

 direction. In many cases the joints of which they 

 consist form a series of little knobs, giving the an- 

 tennae a necklace-like appearance; in others each 

 joint is furnished with a slender process, and the 

 whole organ forms a sort of comb. Occasionally the 

 antennae are beset with long hairs, when they look 

 like little feathers. The joints are sometimes equal 

 in length, and similar throughout, but, as a general 

 rule, those nearest the base are the longest. In some 

 insects the joints of the apex are so much thickened, 

 that the antennae are regularly clubbed; in others 

 these joints form broad flattened plates, which lie 

 close together like the leaves of a book. In short, 

 the variety of form which we meet with in these 

 organs is almost infinite, and the characters derived 

 from them are exceedingly important. In length also 

 the differences presented by the antennae in different 



