66 THE EVOLUTION OF THE BEE. 



pedigree, for it links insects to crabs. The forms placed 

 below the Zoea branch do not pass through the Zoea stage 

 while those above do, or at least they show some modification 

 of the stage. 



Before leaving the crabs let me draw attention to the 

 method of growth which is common to both crabs and insects. 

 I mean that of forming a hard skin or protection and getting 

 out of it when increasing in size or when changing in form. 

 This peculiarity would alone show an affinity between these 

 apparently dissimilar forms. This necessity comes to insects 

 by inheritance, while many of their peculiar forms result from 

 adaptation. Leaving the Zoea stage we come to intermediate 

 forms which link the Spiders (Arachnida) to the Myriopoda 

 and Hexapoda, or to the orders of numerous legs and those of 

 six legs. These forms, still faintly visible in insect larval 

 development, consisted of head with feelers, thorax with three 

 pairs of legs, and with both gills and air-tubes. The 

 centipedes, though possessing a number of legs, really 

 possess in the egg but three pairs and afterward develop the 

 remainder by a species of budding. But leaving these we 

 find that a portion of the forms possessing gills took to using 

 them for different purposes ; some remained outside the body 

 and ceased to be used as air-tubes, but were used to propel 

 and support the weight of the insect when leaving one pond 

 for another and thus in time became wings. The fact that in 

 the perfect insect only, do wings appear, and that with few 

 exceptions, reproduction is also a function of the perfect 

 insect explains the cause of wings developing from branchiate 

 gills. 



But we must not suppose that the same cause produced 

 the same effect on all known winged insects. The common 

 larval forms, and their remarkable likeness, proves that there 

 must have been a common parental form which led to the 

 different forms now known. These probably were of some 

 aquatic-fly form possessing six legs and four wings, and biting 

 jaws not very different from those of the crabs, scorpions, 

 and spiders. Having now traced out the evolution as far as 

 the fly, the remainder is comparatively easy. 



Great differences of form between the different kinds of 

 caterpillars and grubs exist and need explanation here, as 

 the ordinary observer is apt to attach too much importance 

 to such differences. The different habits of feeding and the 

 natural selection constantly going on have caused those grubs 

 which were exposed to outside influences to change with their 

 surroundings, and have, owing to the double influence of 





