OLFACTORY ORGANS OF WASPS 



br 



Carabus violascens were detected on the maxillary palpi large, plainly 

 microscopical, white disks, which are surrounded with a great num- 

 ber of extremely small teeth. 



Whether the above-described organs on the palpi of beetles should 

 be considered as olfactory or gustatory in their nature can only be 

 determined by means of physiological experiments; they probably 

 receive taste-nerve terminations. 



The Hymenoptera furnished very good material for histological 

 purposes, so that Hauser could not only study the terminal apparatus 

 of the olfactory nerves in the per- 

 fect insect, but also in three differ- 

 ent stages of the pupa. These are 

 described at length, as regards the 

 distribution of the pits and teeth, in 

 Vespa crabro; each joint of the 

 antenna (flagellum) possesses be- 

 tween 1300 and 1400 pits, nearly 

 60 teeth, and about 70 tactile hairs ; 

 on the terminal joint there are more 

 than 200 teeth, so that each antenna 

 has between 13,000 and 14,000 ol- 

 factory pits and about 700 teeth 

 (Kegeln). Fig. 278 represents a 

 cross-section through the penulti- 

 mate antennal joint of Vespa 

 crabro; we can see how thick are 

 the series of openings on the sur- 

 face of the antennae, and how 

 regular is the distribution of the 

 teeth. 



The distribution of the olfactory 

 pits and olfactory teeth is thus 

 seen to be very general ; the deviations are so insignificant that there 

 is no reason for the establishment of more than one type. 



Antennal pits with a small crevice-like opening occur in genera 

 nearly allied to Vespa and also in most Ichneumonidse, Braconidae, 

 and Cynipidse. But the crevice-like openings in these families are 

 considerably longer and often are of a somewhat twisted shape. In 

 all the species with translucent antennae we can recognize the inner 

 mouth of the pit as a round or nearly round disk situated usually 

 under the middle of the opening. The antennal pits of Apis mel- 

 liftca, as well as those of Bombus (Fig. 280) and allied genera, differ 



FIG. 279. Olfactory pits of the antenna 

 of Yexfa rulgui-is. After Kraepelin. 



