30 



FLY. 



the trachea-like cliannels, and correspond to the similar 

 organs in the bee (Fig. 29, Gs). Each of these resembles 

 a double circle, which scarcely projects, if at all, beyond 

 the general surface, and which he regards as a 

 metamorphosed, hollow, perforated hair. At the base 

 of each organ is a nerve, which at some little distance 

 forms a multicellular ganglion, and the 

 sheath of which, immediately below the 

 skin, forms a delicate and short, but well- 

 marked, chitinous, cylinder. 



It may also be observed, at any rate in 

 most insects, that while they are feeding 

 the palpi hang down motionless, and evi- 

 dently take no part in the operation. 



In reference to the sense of taste, I may 

 also mention that an additional complexity 

 arises from the fact that many insects 

 possess more than one kind of salivary 

 gland, and it is possible, as Wolff sug- 

 gests,* that the secretions may have dif- 

 ferent properties. In addition to this, 

 Wolff thinks he has proved that the 

 character of the secretion differs at differ- 

 ent ages; that for many days after the 

 bee has arrived at its imago condition, 

 the glands are still imperfect and gradually 

 increase to their full size. In old bees, 

 again, according to him, the secretion diminishes in 

 quantity. This, perhaps, throws some light on the 

 division of labour. Forel has observed among ants 

 that they remain for some days engaged iu indoor 



Fig. 30. — Organ 

 of taste of fly 

 (Musca vomi- 

 torid') ; after 

 Kraepelin. gn, 

 Kerve;f7^, gan- 

 glion ; axt axe- 

 cylinder ; gc, 

 terminal cylin- 

 der ; gk, termi- 

 nal cone. 



* " Das Eiechorgan der Biene.' 



