140 



EVOLUTION AND GENETICS 



The venation of the wings is based on a definite plan which 

 shows modification in several ways toward greater complexity or 

 simplicity (Fig. 136). 



In all of these structures and in their metamorphosis insects 

 show the possibility of almost infinite modification to fit varied 



environmental conditions. 

 Their diversity is exceeded 

 by no other animals and 

 consequently furnishes an 

 excellent illustration of an 

 actual phylogenetic series. 



Since Handlirsch's studies 

 of insect phylogeny are 

 more nearly complete than 

 those of any other ento- 

 mologist, his table is here 

 reproduced with the popu- 

 lar equivalents for the or- 

 dinal names indicated 

 wherever such terms are 

 available (Fig. 81). It will 

 be noted that the extensive 

 fossil remains of the Car- 

 boniferous and Permian are 

 in only four cases referable 

 to modern orders. All of 

 these creatures are insects, 

 beyond a doubt, but they 

 have almost completely dis- 



FiG. 79.— Palaeozoic insects. A, Sienodichja appeared, leaving a more 

 lobata; B, Eubleptus danield. Both be- or less different fauna to 

 long to the primitive Palae<)dictyoptera. ^ake their places. As the 

 (From Lull, after Handhrsch.) » ,, ... 



names oi the pnmitive or- 

 ders indicate, some resemble modern orders. Others are wholly 

 unlike existing insects except in fundamental structure. 



Such diagrams as this are necessarily based on all available 

 knowledge. Comparative anatomy, embryology, and palaeon- 

 tology alike contribute to the formulation of a reasonably complete 

 result. Since the actual record of evolution is broken we must be 

 content with such information as we can piece together from the 



