210 DISEASES OF INSECTS. 
ing*. Though these benefactors of the human race con- 
stitute numerous genera, at present not well ascertained, 
I shall speak of most of them under the common name 
of Ichneumon. 
The appearance of these little four-winged flies puzzled 
much the earlier naturalists :—that a caterpillar usually 
turning to a moth or butterfly should give birth to my- 
riads of flies, was one of those deep mysteries of nature 
which they knew not how to fathom>: even the pene- 
trating genius of our great Ray, though he ultimately 
ascertained the real fact‘, was at one time here quite at 
fault; for he seems at first to have thought, when from 
any defect or weakness nature could not bring a cater- 
pillar to a butterfly, im order that her aim might not be 
entirely defeated, that she stopped short, and formed 
them into more imperfect animals4. 
Before I detail more particularly the proceedings of 
Ichneumons, I shall make a few genera] remarks upon 
them. ‘The structure of the instrument by which they 
are enabled to deposit their eggs in their appropriate 
station has been before sufficiently described *; it is long 
or short according to the situation and circumstances of 
the larva which receives them : if it lives in the open air, 
and the access to it is easy, it is usually short and re- 
tracted within the body; but if it lies concealed in deep 
holes or cavities, or shuns all approach, it is often very 
long. Thus in Pimpla Manifestator, which commits its 
eggs to the grub of a wild bee inhabiting the bottom of 
deep holes bored in posts and rails, the ovipositor is 
* Reaum. ii. 439. " Ibid. 415. Mouffet 57. 
© Hist. Ins. Preef. xv. 4 Cat. Cant. 137. 
© See above, p. 154—. 
