INSECTS IN GENERAL 15 



in unbroken succession from the much simpler forms 

 of life which inhabited the earth in the remote past. 

 We have already seen that insects appear to have 

 been derived from a worm-like ancestral stock. This 

 much is admitted by all those who are qualified to 

 speak ; and when these authorities agree to alter the 

 classification of insects in any way, this means that 

 they have made a fresh discovery. They have un- 

 earthed some evidence of relationship hitherto obscure, 

 and are thus able to add to our knowledge of insect 

 lineage. We must bear in mind, however, that all 

 schemes of classification must be somewhat artificial, 

 because for the sake of convenience we have to group 

 together those kinds of insects which seem to be most 

 nearly akin. These groups have no real and separate 

 existence in the long sequence of insect life upon the 

 earth. Just as past, present, and future become 

 merged in eternity, so the countless generations of 

 insects which have succeeded one another since the 

 race began combine to form one immense family tree. 

 For the method of classification now in use we are 

 indebted to the great Swedish botanist, Carl von 

 Linne, or Linnaeus, as he is often called. He gave 

 names to all the kinds, or species, of plants and animals 

 that were known to him, and assembled the species 

 which seemed to resemble each other most closely 

 into little groups, each of which he called a genus. 

 In this way every species received two names a 

 generic name, common to the group, and a specific 

 name, exclusive to the particular plant or animal con- 

 cerned. Take, for example, our three common black 

 and white butterflies, which belong to the genus 

 Pieris. The large white is called Pieris brassica, the 

 small white Pieris rapa, and the green-veined white 



