STRUCTURE AND CLASSIFICATION. 



45 



It is probable that in the antennae we have a sense of percep- 

 tion which is able to discriminate between atmospheric vibrations, 

 and in this way the same or similar structures may serve as organs 

 of hearing, smell, and touch. That is to say, it is probable that 

 there is no such sense in insects as the power to discriminate 

 between smells, but that each is able to recognize certain definite 

 kinds of odors which do produce an effect upon it. So it is also 

 likely that only sounds of certain descriptions are recognized, 

 and these sounds may even be such as the human ear is not 

 capable of perceiving. We are far from understanding the senses 

 of insects, but the above outline is all that is necessary for our 

 present purpose. 



CHAPTER VII. 



THE REPRODUCTIVE SYSTEM. 



The rate of increase among insects is often very great. It is 

 nothing unusual to hear a farmer say that on one day his plants 

 were free from insects, or nearly so, while a week thereafter 

 everything seemed to be swarming. As a matter of fact, this is 

 frequently due to a failure to observe the insects in the first place, 

 either in the stage in which they then existed or on account of 

 their small numbers ; but it remains true, nevertheless, that in- 

 sects are often exceedingly prolific. The number of eggs laid 

 by a female often runs up to one thousand, or even more, while 

 the number of eggs within the power of a Termite queen is be- 

 yond all calculation. If it were not for their natural checks, in- 

 sects would soon overrun the world. In one year not one green 

 thing would be left on the face of the earth, and not one living 

 being other than insects would exist. These natural checks con- 

 sist largely in sudden changes or abnormally high or low tem- 

 perature, in unusual moisture or drought, or in a combination 

 of two or more of these factors. Diseases often attack insects, 

 and genuine epidemics occur, sweeping off millions in one stage 

 or the other. The natural enemies are legion ; many vertebrates 

 are largely dependent for their food upon insects, and this is 

 especially true of birds and reptiles, some of which subsist upon 

 insects exclusively. A large proportion of the insects themselves 



