1868.] PARKES— RESPIRATION OF INSECTS. 423 



therefore, in tins paper to do more than indicate the prevailing 

 structure. And first, with regard to the spiracles, or external 

 breathing organs of these creatures. If you will examine the 

 body of almost any insect, you will perceive, arranged along each 

 side of the abdomen and thorax, a series of openings, each bounded 

 by a dark colored ring. The office of these, is to admit air to 

 the interior of the animal's body, and to regulate its admission 

 and expulsion according to existing circumstances. The 

 essentials of these spiracles appear to be, 1st, a marginal ring of 

 horny or cartilaginous substance, capable of being opened and 

 closed by an arrangement of muscles, (thus forming the frame- 

 work of the spiracle, and serving as a support to the delicate 

 tubes within) ; and 2nd, a variously arranged membrane, or fringe, 

 or system of horny plates, placed within this horny ring, for the 

 purpose of preventing the entrance of dust or other matter, which 

 might stop up the air passage within, and thus cause the death of 

 the animal. The number of these spiracles, possessed by different 

 insects, varies of from two to eighteen ; the number frequently 

 differing in the same insect, according as it is in its larval or per- 

 fect state. Iu every order (as before observed) there is some 

 peculiar modification in the structure of this important organ ; 

 and even striking variations in different members of the same 

 order, as will be seen in the specimens sent to illustrate this paper. 

 It is supposed by some entomologists, that some of these spiracles, 

 (namely, the abdominal ones,) are specially concerned in the 

 inspiration of air ; and that those situated in the thorax are 

 designed for its expulsion. The point most worthy of notice and 

 admiration, however, in the structure of these orgaus is, the 

 perfect and exquisitely beautiful manner in which provision is 

 made for the protection of the elaborate system of vessels to which 

 they lead. In some beetles, peculiarly liable to be infested by 

 parasites, (which parasites attach themselves to the softer parts 

 of the body where the spiracles are placed,) there is a membranous 

 covering with a narrow opening, thickly studded with sharp spines. 

 In others, whose habits are of a burrowing character, we fiud the 

 entrance guarded by an admirable arrangement of horny or 

 cartilaginous plates, while in many of the dipterous and neurop- 

 terous insects, there is an elegant arrangement of fringed 

 processes, which, for beauty as microscopic objects, can scarcely 

 be surpassed. Some writers have supposed that the humming or 

 buzzing noises made by many insects, when on the wing, is pro- 



