STKUCTURE AND CLASSIFICATION. 



19 



Fig. 6. 



tions, securing a small amount of fine shreds and scraps. These it 

 moistens with a drop of saliva, which has great solvent properties, 

 and then draws up the mixture by means of a sucking or pump- 

 ing stomach. Liquids are taken in the same way, and the insects 

 may be said to lap as well as suck their food. Flies as adults are 

 not injurious to vegeta- 

 tion, whatever may be 

 said of their larvae ; but 

 some of those fitted for 

 piercing, like the mos- 

 quitoes, horse-flies, and 

 gnats, are often trouble- 

 some or injurious to 

 stock, and occasionally 

 render regions infested 

 by them scarcely habit- 

 able for man. 



The bees seem to 

 combine the features of 

 a biting and sucking 

 mouth ; the mandibles 



being fully developed and the labium greatly elongated, that they 

 may gather the nectar upon which they feed and which they 

 store, even from the deepest flowers. This modification will be 

 more fully described in speaking of the bees themselves. 



All the types of mouth structures above described and figured 

 are derived from one original form by gradual modifications of 

 the different pieces ; but this can be traced only in a long series 

 of preparations from many different families and species. 



Next to the mouth parts, the most important appendages of 

 the head are the antennae or feelers. These are variable in form, 

 and in certain orders their structure indicates, unfailingly, the 

 food habits of the insect. They are made up of a variable num- 

 ber of joints, differing greatly in their proportion to each other, 

 in their shape, and in their functions. Ordinarily the antennae 

 are intended as tactile organs, — that is, for touching, as the com- 

 mon name "feeler" indicates; but it is very certain that other 

 sensory structures are also located there. The perception of 

 odors, or the sense of smell, is a very important function, and 



Piercing mouth structures of a "horse-fly": the 

 sucking lip is omitted. Much enlarged. 



