THE ANATOMY OF INSECTS. 



37 



organs of insects that are generally believed to be ears are the 

 so-called tympanal organs of Orthoptera, which are placed at the 

 sides of the first abdominal segment in the Acrididae, and near the 

 proximal end of the tibiae of the first pair of legs in the Locustidas 

 and Gryllidae ; and even in the case of these it is not proven that 

 they have the function of hearing. 



As to the sense of smell many conflicting views are held ;* but 

 the weight of opinion now is that certain antennal structures are the 

 organs of smell. These structures are to be found in the antennae 

 of many insects. If, for example, the surface of the plates that com- 

 pose the club of the antennae of a May-beetle be examined it will 

 be found to be thickly studded with pits. These can be seen with a 



XfJfe- 



— hi 



Fig. 46.— Organ of smell of Fig. 47.— Organ of smell of Fig. 48— Organ of Smell of 



Caloptenus. (After Hau- May-beetle. (After Hau- Vespa. (After Hauser.) 



ser.) ser.) 



Lettering 0/ Figs. 46, 47, and 48.— aa, circular thickening of the skin surrounding the opening of the 

 olfactory pit; br, bristle; ch, chitinous integument of ihe antennae; /, invaginated pit; hyc, hypo- 

 dermic cells; i, entrance into the canal belonging to the pit; m, olfactory membrane; >nc, membrane- 

 forming cell; «, nerve of special sense; nc. nucleus of the sense- or ganglion-cell ; 0, opening into 

 the olfactory pit; /, olfactory pit; pw, wall of the pit; sc, sense- or ganglion-cell; st, olfactory or 

 sense-style, sometimes peg-shaped. 



microscope of low power; but in order to determine the minute 

 structure of the organs thin sections of them must be made and ex- 

 amined with high powers. Fig. 47 represents a section of one of 

 these pits ; and Figs. 46 and 48 represent the corresponding organs 

 in a locust and in a wasp.f The form of these organs of smell varies 



* See Packard's abstract of a paper upon this subject by Dr. K. Kraepelin, American 

 Naturalist, 1886, pp. 8S9 and 973. 



f See Hauser, On the Organs of Smell in Insects, translated by Packard, American 

 Naturalist, 1887, p. 279. 



