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ANATOMY AND PHYSIOLOGY 



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hairs from the two larger of the four caudal appendages of a cricket, 

 Gryllus; some of these (Fig. 136) may be olfactory, though possibly 

 tactile. The same author found on the terminal palpal segment in 

 various Lepidoptera a large flask-shaped invagination (Fig. 137) into 

 which project numerous 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. 



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 ex- 

 ample, are olfactory, it frequently hap- 



FIG. 134. Section through antennal olfactory 

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

 pb, protecting bristles; s, sensory cell. After 

 HAUSER. 



FIG. 135. Longitudinal section of 

 antennal olfactory organ of wasp, 

 Vespa. c, olfactory cell; en, olfactory 

 cone; ct, cuticula; h, hypodermis cells; 

 n, nerve; r, rod. After HAUSER. 



pens that the antennae bear several distinct forms of sensory end-organs, so 

 minute and intermingled that their physiological differences can scarcely 

 be ascertained by experiment but must be inferred from their peculiar! ties 

 of structure. Schenk, however, has arrived at precise results by compar- 

 ing the antennal sensilla in the two sexes, selecting species in which the 

 antennae exhibit a pronounced sexual dimorphism, in correlation with sex- 

 ual differences of behavior. Taking Notolophus antiqua, in which the 

 male seeks out the female by means of antennal organs of smell, he 

 finds that the male has on each antenna about 600 sensilla cceloconica 

 and the female only 75; similarly in the geometrid Fidonia, in which 

 the ratio is 350 to 100. The sensilla styloconica also, of these two 

 genera, are regarded as olfactory organs. These two kinds of end- 



