6 THE INSECT WORLD. 



During their different movements, insects move their antennae 

 more or less, sometimes slowly and with regularity, at other times 

 in all directions. Some insects impart to their antennae a perpetual 

 vibration. During flight they are directed in front, perpendicular 

 to the axis of the body, or repose on the back. 



What is the use of the antennas, resembling, as they do, feathers, 

 saws, clubs, &c. ? Everything indicates that these organs play -a 

 very important part in the life of insects, but their functions are 

 imperfectly understood. Experience has shown that they only play 

 a subordinate part as feelers, and have nothing to do with the 

 senses of taste or smell. There is no other function for them to 

 fulfil except that of hearing. 



On this hypothesis the antennae will be the principal instru- 

 ments for the transmission of sound waves. The membrane at 

 their base represents a trace of the tympanum which exists among 

 the higher animals. This membrane then will be an auditory 

 nerve. 



Situated intermediately between the inferior animals, whose 

 functions more or less resemble those of plants, and the vertebrates, 

 whose functions are localised in a very high degree, insects have 

 received, like these latter, special organs for nutrition. The mouth 

 is the most exterior of these apparatuses. 



The mouth of insects is formed after two general types, which 

 correspond to two kinds of requirements. It is suited in the one 



case to break solid substances, in the 

 other to imbibe liquids. 



At first sight there seems no simi- 

 larity between the mouth of a grind- 

 ing insect and of one living by 

 suction. But on examination it is 

 found that the parts of the mouth 

 in the one animal are exactly ana- 

 logous to the same parts in the other, 

 rig. 5. Mouth of a masticating and that they have only undergone 



modifications suiting them to the 

 different purposes which they have to fulfil. 



The mouth of a breaking insect is composed of an upper lip, a 

 pair of mandibles, a pair of jaws, and a lower lip (Fig. 5). 



