594 THE SENSES AND SENSORY ORGANS. 



Duponchel [262a] regarded the antennae as hygroscopic 

 organs ; but Rath [133J says there is no proof of any such 

 function. Watery vapour has many of the physical properties 

 of odorous bodies, more especially in its relations with radiant 

 energy (Tyndall). It is, however, clear that it could not excite 

 the olfactory membrane of Vertebrates, since this is always 

 surrounded by air, saturated with aqueous vapour, and is itself 

 moist. The end organs of an insect's antennae are, however, 

 placed under very different conditions. That they can act as 

 hygroscopic bodies in the physical sense is extremely im- 

 probable, since the hypodermis would certainly prevent their 

 ever becoming dry enough to absorb moisture like a dried 

 vegetable or animal fibre ; but there is no reason why the 

 nerve end organs should not be stimulated by a moist atmo- 

 sphere. 



It has long been argued that Bees and other Hymenoptera 

 discover the approach of rain by the hygroscopic condition of 

 the atmosphere ; and I have made a series of careful observations 

 on the House Cricket (Acheta domestica). It is well known 

 that these insects drink with avidity, and cannot live long with- 

 out a supply of water. I have repeatedly kept Crickets under a 

 glass shade for months, supplying them with food and water. 

 When the supply of water is withdrawn for two or three days, 

 even in winter, and for a less time in summer, these insects 

 become very thirsty. I introduce a supply of water in a watch- 

 glass, concealed in a cardboard tray, so that it cannot be seen 

 by the insect. The antennae are at once raised, the insect 

 runs about and soon finds the water, always seeking it by sway- 

 ing its antennae. As soon as these organs are brought near 

 the water, the insect goes straight to it. Crickets which have 

 n freshly captured, and kept a day or two without water, 

 lind it almost directly; and I have observed in cold weather 

 th.it they first seek it close to the glass bell, where the vapour 

 condenses most rapidly, but in a few minutes or less go straight 

 to the \vati-r. The manner in which the antennae are moved 

 and the rapidity with which the insects find the water imme- 

 diately after the tips of the antenna.- come vertically over the 



