CONTENTS xv 



among mating animals — Battles to ensure the healthiest 

 mating among spiders, fish, birds, and mammals — Testing 

 oi the powers in drones of the bee and males of other 

 insects — Unequal severity of the test for survival among 

 young males in contrast lo the young females of many 



animals 190 



Eggs and young — Migration — The sea as a nursery — The 

 advantages of pelagic larval life — Modes of defending the 

 eggs and young of aquatic animals by fixing them to some 

 holdfast and by the guardianship of the parents — The nests 

 and nurses of fish — The protection of the eggs by frogs and 

 reptiles — The secretiveness of birds and insects in their 

 choice of nesting sites — Brief review of the nests of birds — 

 Small birds construct the most carefully woven nests — The 

 significance of the relation between size and incubating 

 heat — The varied methods employed by insects — The 

 elaboration of nurseries by social insects .... 201 



CHAPTER X 



THE LIFE-HISTORIES OF INSECTS 



The influence of climate in stimulating the development of 

 insect life — The cyclic changes of its abundance — The 

 insects of early spring — Selection of nesting sites — Differ- 

 ences between families of great and of lesser antiquity in the 

 food of the young 217 



The life- histories of primitive insects — The spring-tails and their 

 allies — The straight-winged insects — Grasshoppers, locusts 

 — The difficulty of shedding the old skin — The development 

 a gradual one — The life-history of the dragon-fly — May-flies 

 and their larvae 222 



More complex life-histories — Metamorphosis — The introduc- 

 tion of the pupal stage — Caddis-flies and caddis-larva- — 

 The development of the pupal stage and the emergence of 

 the fly — Beetles — The life-history of the oil-beetle . . 234 



The life-histories of more modern insects — Butterflies and 

 their adaptations to aerial life — The development of the 

 cabbage-white butterfly — Complex structural changes 

 during the pupal stage — The Diptera or two-winged flies — 

 Their economic importance — The mosquito and midge 



