THE ORGANS OF SMELL. 47 



terminal perfora-tioa, or project as free threads. 

 They differ, again, between themselves, Insects being 

 as a general rule aerial, and Crustacea aquatic. 



Erichson* has the merit of having been the first 

 to support this theory by anatomical examination. 

 Newport had previously mentioned the existence in 

 many insects of certain pits, or *' pores," closed by a 

 delicate membrane, and which he regarded as the seat 

 of hearing. Erichson extended his observations, and 

 suggested that the pits were rather to be regarded as 

 organs of smell. His descriptions were contirmed by 



Fig. 34.— Antenna of Pontella Bairdii (Lubbock). 



Burmeister, who, moreover, detected in some of these 

 " pits "the presence of a small knob, or hair. 



In 1853 I called special attention to the antennae 

 of certain Crustacea, distinguishing five kinds of 

 hairs — (1) short, downy hairs; (2) plumose hairs; (3) 

 cylindrical, tapering hairs; (4) flattened, lanceolate 

 hairs ; (5) wrinkled hairs — and pointed out that they 

 were by no means scattered indiscriminately, but 

 arranged in definite situations, indicating special 

 functions. The two last I was disposed to regard 

 as sense-organs. The above is a figure of the right 

 male antenna of Pontella Bairdii, one of the Cope- 

 * " De Fabrica et usu Autennarum in Insectis." 1847. 



