ANTENNAL ORGANS OF INSECTS. 57 



3. Flattened hairs (Fig. 43, e). 



4. Depressed hairs (Fig. 43, /). 



5. Pits with a minute hair at the base (Fig. 43, g). 



6. Pits without a hair at the base (Fig. 43, h). 



7. Cones containing a nerve (Fig. 43, I). 



8. The champagne-cork-like organs of Forel (Fig. 

 43, i). These consist of a pit, with a constriction about 

 halfway up. They differ, in fact, from the second 

 sort mainly in the presence of this constriction. 



9. The curious flasks (Fig. 43, h) first observed 

 and described by Hicks.* " They consist," he says, " of 

 a small pit leading to a long delicate tube, which, 

 bending towards the base, dilates into an elongated 

 sac having its end inverted." f Of these remarkable 

 organs there are about twelve in the terminal segment, 

 and one or rarely two in the others. Similar structures 

 have since been found in other Hymenoptera ; but not, 

 I believe, as yet in any other order of insects. I have 

 ventured to suggest that they may serve as microscopic 

 stethoscopes. Kraepelin was disposed to regard them 

 as glands, but I agree with Forel that there is no suffi- 

 cient reason for doing so. 



There may, moreover, be a distinctly characterized 

 sense-organ without any alteration of the actual 

 surface, as shown in some of the figures given by 

 Kraepelin, and also by that from Hauser given above 

 (Fig. 42). 



These are, perhaps, the principal types, but there 



* Transactions of the Linnean Society, vol. xxii. p. 39. Kraepelin 

 attributes the observation to Forel, but this is an error. Forel had 

 overlooked Hieks's description and figure. 



t Hicks, " On the Organs of the Antennce of Insects," Transactions 

 of the Linnean Society, vol. xxii. 



