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