344 '^HE BIOLOGY OF INSECTS 



** Panorpoid Complex." It is certain that the inter- 

 relationship of these orders is closer than their kinship to 

 the Hymenoptera, and that for a common origin we must 

 certainly go back to the Carboniferous Period ; but stronger 

 evidence is required than any yet available to establish the 

 independent origin of '' complete " metamorphosis in two 

 of these ancient insect groups. A common, if far off, 

 ancestry for the Hymenoptera and the Lepidoptera is 

 suggested by the close resemblance shown in the arrange- 

 ment of the bristle-bearing tubercles on the body-segments 

 of the larvae in the two orders. Such a detail of structure 

 as this is stronger evidence of relationship than the outward 

 similarity in the caterpillar type of larva common to moths 

 and sawfiies, which may probably be due to adaptation to 

 similar conditions of life. 



There remains only one large order of the Endopterygota 

 to be considered in this survey of relationships — the Coleo- 

 ptera or beetles, which with their biting jaws and fore- 

 wings modified into firm sheaths (elytra) form one of the 

 most distinct and characteristic of all the orders of insects. 

 Geologically, beetles are of considerable antiquity, far older 

 than the Diptera, Lepidoptera, or higher Hymenoptera, as 

 fossils referable to existing families have been found in the 

 early Secondary (Triassic) rocks of Europe, including 

 weevils (Curculionidae) and leaf-beetles (Chrysomelidae) 

 both specialised groups. Among the fossil insects of the 

 Upper Trias of Queensland lately studied by Tillyard, 

 " Coleoptera are dominant, making 46 per cent, of the 

 total fauna." Many of these belong to the Hydrophilidae. 

 Beetles are also represented, though much more sparingly, 

 in the older Upper Permian rocks of New South Wales ; 

 and in these deposits Tillyard has discovered along with 

 the beetles, ** a most remarkable series of larger forewings 

 evidently allied to them and showing all gradations from a 

 flattened, apically pointed tegmen with complete venation 

 down to half-formed elytra with the venation completely 

 lost except in the anal region. These must be regarded as 

 being remnants of the older order from which the true 



