DISEASES OF INSECTS. 211 
nearly an inch and half in length, and in some extra- 
European species three inches. How the egg is pro- 
pelled so as to pass in safety from the oviduct, along this 
extended and very slender instrument to the grub for 
which it is destined, has not been certainly ascertained ; 
but from an observation of Reaumur’s* it should seem 
that it is aided in its passage by some fluid ejected at the 
same time with it, or is so lubricated as to slide easily with- 
out being displaced. ‘The flies we are speaking of by 
some authors are called Musce vibrantes, because when 
searching for the destined nidus of their eggs their an- 
tennee vibrate incessantly, and it is by the use of these 
wonderful organs that they discover it wherever it lurks. 
Bergman observed that Panus Jaculator searches for the 
latent grub of certain bees and other Hymenoptera with 
its antennee®: and from Mr. Marsham we learn that 
Pimpla Manifestator, before it inserts its ovipositor in the 
nest of the grub of Chelostoma mavillosa, explores it first 
with one antenna and then with the other, plunging 
them all the while intensely quivering up to the very root‘. 
With respect to their size, Ichneumons vary greatly; 
some being so extremely minute as to be invisible to the 
naked eye, unless moving upon glass; while others, as to 
their Jength, emulate the giants amongst insects. The 
former, unless appropriated to the eggs themselves, usu- 
ally commit many eggs to a single larva, while the latter 
are directed by their instinct to introduce into them only 
one. Some of the former description are endowed with 
_ the faculty of leaping’. The food of Ichneumons, and 
* Reaum. vi. 306. > Fn. Suec. 1626. 
© Linn. Trans. iti. 26. 4 De Geer i. 608. Linné has 
made a mistake with regard to the Ichneumon here alluded to, in 
calling De Geer’s saltatorious Ichneumon J. Muscarum, and referring 
PQ 
