38 ANTS AND SOME OTHER INSECTS. 



in the antennae. A less important adjunct to these organs is located, 

 as Nagel and Wasmann have shown, in the palpi. In the antennae 

 it is usually the club or foliaceous or otherwise formed dilatations 

 which accommodate the cellular ganglion of the antennary nerve. 

 I shall not discuss the histological structure of the nerve-termina- 

 tions but refer instead to Hicks, Leydig, Hauser, my own investi- 

 gations and the other pertinent literature, especially to K. Kraepe- 

 lin's excellent work. I would merely emphasise the following 

 points : 



1. All the olfactory papillae of the antennae are transformed, 

 hair-like pore-canals. 



2. All of these present a cellular dilatation just in front of the 

 nerve-termination. 



3. Tactile hairs are found on the antennae together with the 

 olfactory papillae. 



4. The character and form of the nerve-terminations are highly 

 variable, but they may be reduced to three principal types: pore- 

 plates, olfactory rods, and olfactory hairs. The two latter are 

 often nearly or quite indistinguishable from each other. The nerve- 

 termination is always covered with a cuticula which may be never 

 so delicate. 



Other end-organs of the Hymenopteran antenna described by 

 Hicks and myself, are still entirely obscure, so far as their function 

 is concerned, but they can have nothing to do with the sense of 

 smell, since they are absent in insects with a delicate sense of smell 

 (wasps) and accur in great numbers in the honey-bees, which have 

 obtuse olfactories. 



That the antennae and not the nerve-terminations of the mouth 

 and palate function, as organs of smell, has been demonstrated by 

 my control experiments, which leave absolutely no grounds for 

 doubt and have, moreover, been corroborated on all sides. Ter- 

 restrial insects can discern chemical substances at a distance by 

 means of their antennae only. But in touch, too, these organs are 

 most important and the palpi only to a subordinate extent, namely 

 in mastication. The antennae enable the insect to perceive the 

 chemical nature of bodies and in particular, to recognise and dis- 



