8o 



ENTOMOLOGY 



(Hicks). The male of Melolontha vulgaris, which seeks out the female by 

 the sense of smell, has according to Hauser 39,000 pits on each antenna, 

 and the female only 35,000. Pits presumably olfactory in function have 

 been found by Packard on the maxillary and labial palpi of Perla and 

 on the cerci of the cockroach, Periplaneta americana. Vom Rath has de- 

 scribed four kinds of sense hairs from the two larger of the four caudal 

 appendages of a cricket, Gryllus; some of these (Fig. 134) may be olfac- 

 tory, though possibly tactile. The same author found on the terminal 

 palpal segment in various Lepidoptera a large flask-shaped invagina- 

 tion (Fig. 135) into which project numer- 

 ous chitinous rods, each a process of a 

 sensory cell, which is supplied by a 

 branch of the principal palpal nerve; 

 these peculiar organs are inferred to be 

 olfactory. 



FIG. 132. Section through antennal olfactory 

 pit of fly, Tabanus. c, cuticula; p, pit with peg; 

 pb, protecting bristles; s, sensory cell. After 

 HAUSER. 



FIG. 133. Longitudinal section of 

 antennal olfactory organ of wasp, 

 Vespa. c, olfactory cell; en, olfactory 

 cone; c/, cuticula; h, hypodermis cells; 

 n, nerve; r, rod. After HAUSER. 



The chief reason for regarding these various end-organs as olfactory is 

 that they appear from their structure to be better adapted to receive that 

 kind of an impression than any other, so far as we can judge from our own 

 experience. Though it is easy to demonstrate that the antennae, for 

 example, are olfactory, it frequently happens that the antennae bear sev- 

 eral distinct forms of sensory end-organs, so minute and intermingled 

 that their physiological differences can scarcely be ascertained by experi- 

 ment but must be inferred from their peculiarities of structure. Schenk, 

 however, has arrived at precise results by comparing the antennal sen- 

 silla in the two sexes, selecting species in which the antennae exhibit a pro- 

 nounced sexual dimorphism, in correlation with sexual differences of be- 

 havior. Taking Notolophus (Orgyia) antiqua, in which the male seeks out 



