13

6. _Aphis pomi_, winged and wingless females 19

7. Mussel Scale-Insect (_Mytilaspis pomorum_) 21

8. Emergence of Dragon-fly (_Aeschna cyanea_) 29-31

9. Nymph of May-fly (_Chloeon dipterum_) 33

10. Imaginal buds of Butterfly 39

11. Imaginal buds of Blow-fly 43

12. Carrion Beetle (_Silpha_) and larva 51

13. Larva of Ground-beetle (_Aepus_) 52

14. Willow-beetle (_Phyllodecta_) and larva 53

15. Cabbage-beetle (_Psylliodes_) and larva 54

16. Corn Weevil (_Calandra_) and larva 55

17. Ruby Tiger Moth (_Phragmatobia fuliginosa_) 61

18. Larvae and Pupa of Hive-bee (_Apis mellifica_) 65

19. Larva of Gall-midge (_Contarinia nasturtii_) 68

20. Crane-fly (_Tipula oleracea_) and larva 69

21. Maggot of House-fly (_Musca domestica_) 71

22. Ox Warble-fly (_Hypoderma bovis_) with egg,
larva, and puparium 75

23. Pupa of White Butterfly (_Pieris_) 85

CHAPTER I

INTRODUCTION

Among the manifold operations of living creatures few have more strongly
impressed the casual observer or more deeply interested the thoughtful
student than the transformations of insects. The schoolboy watches the
tiny green caterpillars hatched from eggs laid on a cabbage leaf by the
common white butterfly, or maybe rears successfully a batch of silkworms
through the changes and chances of their lives, while the naturalist
questions yet again the 'how' and 'why' of these common though wondrous
life-stories, as he seeks to trace their course more fully than his
predecessors knew.

[Illustration: Fig. 1. _a_, Diamond-back Moth (_Plutella
cruciferarum_); _b_, young caterpillar, dorsal view; _c_, full-grown
caterpillar, dorsal view; _d_, side view; _e_, pupa, ventral view.
Magnified 6 times. From _Journ. Dept. Agric. Ireland_, vol. I.]

Everyone is familiar with the main facts of such a life-story as that of
a moth or butterfly. The form of the adult insect (fig. 1 _a_) is
dominated by the wings--two pairs of scaly wings, carried respectively
on the middle and hindmost of the three segments that make up the
_thorax_ or central region of the insect's body. Each of these three
segments carries a pair of legs. In front of the thorax is the head on
which the pair of long jo