892 



INSECTA. 



curious organs, the necessity of which it is 

 difficult to understand. 



The Junction of the antenna: has been a 

 subject of much dispute amongst naturalists, 

 some contending that it is simply that of feel- 

 ing, others that of smelting, others again that 

 of hearing, and lastly others that of a sixth 

 sense unknown to vertebrata. Our own ob- 

 servations lead us most decidedly to the con- 

 clusion that the primary function of the an- 

 tennae is that of hearing or feeling the vibra- 

 tions of the atmosphere, while an additional 

 function possessed by the antenna of many 

 insects is that of common feeling or touch. 

 We have endeavoured to support this opinion 

 by facts and experiments detailed in a paper 

 on the use of the antenna, which was read 

 before the Entomological Society of London 

 in the beginning of 1838, but which has not 

 yet been printed. First as regards the employ- 

 ment of the antenna; as olfactory organs, there 

 seems in their anatomical structure the most 

 decided evidence that they cannot be designed 

 for such purpose. In every instance in verte- 

 brata, the faculty of smelling is situated in a 

 delicate mucous or soft surface, and in no 

 animal that we are aware of has it ever been 

 found to reside in a dry horny covering, or in 

 a tense membranous structure, while, on the 

 contrary, that of hearing is constantly depen- 

 dent upon an elastic membrane, or other part 

 sufficiently delicate to be affected by the vibra- 

 tions of the atmosphere. If therefore the sense 

 of smelling be dependent, as it appears to be, 

 upon a moist or lubricated surface, it cannot 

 reside in the antenna, since the exterior sur- 

 face of these organs is in every instance formed 

 of a dry hardened covering. On the other 

 hand, if the perception of sound be depen- 

 dent upon the elasticity of a part, and its capa- 

 bility of being affected by the vibrations of the 

 air, the structure of the antennae is in no in- 

 stance unadapted for the performance of this 

 function. It seems improbable that the office 

 of the antenna is simply that of touching or 

 feeling other objects, by direct contact, as sup- 

 posed by some naturalists, from the circum- 

 stance that in certain insects these organs are 

 much too short to be so employed, being in 

 many species, as in the Libetlulida and Cica- 

 diidae (Jig. 353), shorter than the head itself. 

 But that they are so employed by some insects 

 is indisputable, particularly by the Blattidg, 

 Gryllidtf, and most of the Hymenoptera. 

 The Gryllida, when sipping water from the 

 channelled surface of a moistened leaf, con- 

 stantly feel about with the antenna ; and the 

 honey-bee, when constructing its cells, ascer- 

 tains their proper direction and size by means 

 of the extremities of these organs, while the 

 same insect, when evidently affected by sounds, 

 keeps them motionless in one direction, as if 

 in the act of listening. Another circumstance 

 which favours the opinion that they are audi- 

 tory organs is their greater development in the 

 males of some species than in the females, as 

 in the bipectinated antennae of many moths, 

 and the lamellated ones of the Metolonthidit. 

 The structure well known to exist in the 



Crustacea,* the bony tubercle covered exter- 

 nally by a tense membrane, and communi- 

 cating internally with a membranous vesicle, 

 situated at the base of the antenna, sufficiently 

 proves that in those animals the antenna are or- 

 gans of hearing, and is not an inadequate reason 

 for regarding them as ministering to the same 

 function in insects. But the fact of the ex- 

 istence of a small circular space discovered by 

 Treviranus, at the base of each antenna in the 

 Rlattida., (fig. 373, t) which are noted for 

 extreme acuteness of hearing, and which space, 

 as in Crustacea, is covered by a membrane, is 

 an additional reason for considering the func- 

 tion of the antenna in insects analogous to 

 that of the corresponding organs in those 

 animals. Thus then almost every circumstance 

 connected with the antenna leads us to the 

 conclusion that these are the proper organs of 

 hearing, while their occasional employment as 

 factors or cerebral feelers is not incompatible 

 with the exercise of that function, hearing be- 

 ing in reality only a more exquisite sense of 

 feeling. 



Fig. 372. 



Interior of the upper and under surface of the 



head of Hydrous. 



d, clypeus ; e, labrum ; </. maxilla , h, its pal- 

 pus ; t, labium ; k, labial palpus ; p, sutura epi- 

 cranii ; q, cotyloid cavity ; r, torulus ; s,v, laminae 

 squamosaa ; t, lamina: posteriores ; M, tentorium j 

 ), laminae orbitales ; x, os transversum ; y, arti- 

 culating cavity for the mandible ; tt, os hypopha- 

 ryngeum. 



Internal parts of the head. On the interior 

 surface of the superior portion of the cranium 

 of Hydrous piceus (fig. 372), the insect we have 

 selected for our purpose, is a thick horny ridge 

 (p), extending along the middle line from the 



* See vol. i. p. 768, art. CRUSTACEA. 



