138 



INTRODUCTION 



terminal ones, or scattered over the whole surface of the antennae, and consist 

 of bristle-like or conical hairs, pits, and membranous canals. 



According to Kolbe ('Einfiihrung in die Kenntnis der Insekten,' pp. 432-5) 

 the following are the facts with regard to the development of olfactory organs in 

 the various orders of insects. 



Butterflies and Moths possess on their antennae projecting sensory hairs, 

 simple chitinous pits with a single sensory cone, and also large pits with many 



Fig. 54. Olfactory organs of Insects, a, Transverse section through the wall of the antenna of 

 the Cockchafer. iV, nerve ; Ch, chitinous membrane ; G, ganglion-cell of the sensory cone {Sk) sunk in 

 a pit. b. Section through the antenna of Cetonia aurata. References as in a. (After O. vora Rath.) 



such cones. The sensory hairs are large, pale, chitinous tubes, which are 

 generally somewhat curved, and more or less tapering. The simple pits present 

 a great variety in structure and are generally distributed, while the pits with many 

 sensory cones are found only in certain genera. Hawk-moths possess the most 

 specialized olfactory organs, and Kerner (cf. p. 125) has made observadons with regard 

 to the delicate sense of smell possessed by these insects. 



Upon the antennae of Beetles are to be found superficial sensory cones 

 and sensory bristles, together with membranous canals and chitinous pits (Fig. 54). 



The number of these little sensory pits is par- 

 ticularly large in carrion-loving beetles (Silpha, 

 Necrophorous, Staphylinus, &c.). In the cock- 

 chafer there are 39,000 such pits on the antennae 

 of the male, and 35,000 on those of the female. 

 No pits have hitherto been found in the Carabidae, 

 Cerambycidae, Chrysomelidae, Curculionidae, 

 and Cantharidae. 



Hymenoptera possess membranous canals, 

 various forms of cone, and pointed sensory hairs 

 (Fig. 55). Besides these structures, Forel has 

 found ' flasks ' ^ and ' champagne-cork organs ' 

 in the skin of Ants, Htituble-bees, and Bees. 

 These also are of sensory nature. The ' cham- 

 pagne-cork organs' of humble-bees and bees are confined to the terminal joint. 



Fig. 55. Olfactory organs of Gontpho- 

 ceriis riifus. Part of a longitudinal section 

 through the antenna. Ch, Chitinous mem- 

 brane; Sk, sensory cone ; Gr, sensory pit; 

 <?> ganglion; iV, nerve. (After O. vom Rath.) 



* [These structures were previously described by Hicks, ' On the Organs of the Antennae of 

 Insects,' Trans. Linn. Soc, London, xxii, 1857. Tr.] 



