356 The Pedigree of Insects 



Origin of Metamorphosis. — The fossil remains 

 of iiolometabolous insects resemble so closely those 

 now living that they can be readily considered in our 

 review of the orders to which they belong. It may 

 be mentioned however, that except a few Carboni- 

 ferous fossils referred to the Coleoptera, there is no 

 evidence for the existence of insects with complete 

 metamorphosis before the Secondary epoch. What 

 geological testimony we have, therefore, confirms the 

 impression derived from the study of living insects 

 that the metamorphic orders are the highest. Before 

 surveying these orders it will be well to devote a 

 short space to the difficult question of how insect 

 metamorphosis arose. 



It is well known that a vast number of animals are 

 hatched from the egg in a state very unlike that of 

 their parents, passing through marked changes of 

 form before reaching their full growth. Starfishes, 

 Crabs and Oysters, are sufficiently familiar examples 

 drawn from different great Branches of the animal 

 world. But these are marine animals which produce 

 eggs with a small supply of yolk. Fresh-water 

 animals, as a rule, undergo less marked transforma- 

 tions than their marine relations, while land animals 

 are almost always hatched or born in a form closely 

 like their parents, who produce large eggs with 

 plentiful yolk or otherwise provide for the full 

 development of their offspring. Generally speaking, 

 metamorphosis among animals is confined to dwellers 

 in the water, who produce multitudinous young, and 

 turn them out while still undeveloped to shift for them- 

 selves. The transformations of insects, a typically 

 air-breathing class, present therefore an exceptional 

 and puzzling problem (71)- 



The insect-larva has often been represented as a 

 prematurely hatched embryo which leaves the egg 



