LESSON 42.] NUTRITION IN INSECTS. 147 



LESSON XLII. 



NUTRITION IN INSECTS, CONCLUDED. 



657. In the last order of winged insects, the Diptera, the mouth 

 is again transformed ; here we have a proboscis, or Haustellum, which 

 is membranaceous, or more or less fleshy. It descends in a perpen- 

 dicular direction from the orifice of the mouth, and is, in general, 

 shortly from its origin, kneed (shaped like a knee) forward, and ter- 

 minates in a flapper-shaped, suctorial surface. 



658. In many of the predaceous Diptera (Tabini, Chrysops, 

 Stomoxys, &c.}, the bristles, or lancets lie, in a hollow groove exca- 

 vated in the upper surface of the proboscis, and covered and con- 

 cealed by a long corneous triangular scale, the upper lip. The Mos- 

 quito, Flea, and others, carry their lancets within a case, on the 

 principle of the Hemiptera. 



659. Many of the vegetable feeding two-winged flies, are pro- 



FIG. 242. 







FIG. 243. 



Fleshy under lip of 

 Helophilus tenax. 



Upper part of mouth, Helophilus 

 tenax. 



vided with a mouth, in every respect similar to the Tabini, and their 

 allies (Fig. 242). 



660. The mouth of the rat-tailed worm-fly (Helophilus tenax), 

 to which Swammerdam did such ample justice, is a good illustration. 

 The insect in its perfect state feeds only on ripe fruit, which it first 

 stabs, or wounds, with its lancets, and then withdrawing them, places 

 the expanded fleshy under lip over the wound. 



661. These, moistened with saliva, firmly adhere by means of 



