THE WALKS ABROAD OF 



" In the insects that have two wings, Diptera, the 

 mouth forms a proboscis composed of four parts a 

 sheath, a suctorial apparatus, and two palpi. If you 

 examine, even with a slight magnifying power, the 

 head of a fly, you will be able to recognise these 

 different pieces. Moreover, as they have only two 

 wings, and as it would not be right that they should 

 have fair grounds for being jealous of the better 

 endowed insects, they have instead of the second pair 



TWO-WIXGED FLY (JfllSCa). 



of wings what do you suppose ? Balancers or 

 halteres." 



" Like the rope-dancers at a circus. And what is 

 the use of these organs to them ?" 



"Exactly the same;* and these little instruments 

 are even of more service to them than those of the 

 performers you have mentioned. Have you any idea 

 of the number of strokes a common fly makes with its 

 wings in a second ?' : 



" No doubt many ; here is one on the table, 

 suppose we ask it ?" and stretching out his hand 



* This is not established. Translator. 



