34 A BOOK OF INSECTS 



but there is much evidence to support the view that the 

 head is made up of six segments (three in front of, and 

 three behind, the mouth), the thorax of three, and the 

 abdomen of twelve — twenty-one segments in all. 



The origin of insects' wings, which spring from the 

 second and third thoracic segments, is also a debated 

 point ; but the fact that insects possess these organs, in 

 combination with their other specialised endowments, 

 places them indubitably at the head of the foot-jawed 

 class, and consequently of the whole Appendiculate 

 phylum. Yet we must not infer that each and every 

 insect is more highly specialised than (for example) a crab 

 or a spider. " A shoot arising low down on a branch " (says 

 Professor Carpenter) " may send out twigs which overtop 

 the lower twigs of a shoot whose origin is higher." Thus, 

 while such an insect as a iiy or a wasp represents the 

 "last word" in the evolution of ring-planned, foot-jawed 

 creatures, many of its lowly kindred have by no means 

 attained to this high level of perfection. Among animals 

 that are not insects, ..those which approach most nearly 

 to the insect type are certain centipede-like creatures 

 which belong to a genus called Scolopendrella. They live 

 in damp earth, and similar concealed situations. They 

 are small and fragile, with a pair of antennae, three 

 pairs of foot-jaws, and an evenly segmented body with 

 fourteen pairs of limbs. This, of course, is eleven pairs 

 in excess of those possessed by insects ; but the most 

 lowly of all living insects, the silver-fishes and their 

 allies, actually reveal the vestiges of paired limbs on 

 several of the abdominal segments, while the presence 

 of others is indicated by caudal appendages termed 

 cercopods. 



We thus get some indication of the genealogy of 

 insects. But how were the innumerable changes from 



