20 ENTOMOLOGY 



(Tenthredinidae), judging from their resemblance to mecopterous and 

 lepidopterous larvae; and the simple, maggot-like form of the larvae of 

 ants, bees, wasps and parasitic Hymenoptera is due to secondary modi- 

 fications in correlation with their sedentary mode of life. 



In Diptera and Hymenoptera the phenomenon of metamorphosis 

 attains its greatest complexity, as was remarked. Opinions differ as to 

 which of these two orders is the more specialized. Hymenoptera are 

 commonly called the "highest" insects, when their remarkable psycho- 

 logical development is taken into account; but from a purely structural 

 standpoint it is hard to say which order is the more complex indeed, the 

 two orders are specialized in so many different ways that no precise com- 

 parison can be made between them. 



The following diagram (Fig. 32) is a graphic summary of what has 

 just been said in regard to the genealogy of the orders of insects. The 



SIPHONAPTERA 

 THYSANOPTERA 



HEMIPTERA 

 COLLEMBOLA 



COLEOPTERA THYSANURA 



FIG. 32. Genealogical diagram of the orders of insects. 



positions of Hemiptera and Coleoptera are most open to criticism. The 

 central group (T) is the hypothetical thysanuroid source of all insects, 

 including Thysanura themselves. Though Thysanura and Collembola 

 show no traces of wings, even in the embryo, it should be borne in mind 

 that all the other insects probably had winged ancestors and that it is 

 more reasonable to assume a single winged group as a starting point than 

 to suppose that wings originated independently in several different 

 groups of insects. 



