INTERNAL ANATOMY OF INSECTS. 157 
of Chrysis (C. ignita, &c.), which is covered by several 
demi-tubes or scales enveloping and sliding over each 
other: when these scales are removed, the true ovipositor 
appears, which is of a structure similar to that of the rest 
of the Order, but the valves are long and slender with 
their summit generally visible without the anus?. 
Though the ovipositor of the majority of Dipterous in- 
sects is a tube with retractile joints, in the crane-flies 
this organ is different, and, like that of Acrida above de- 
scribed, consists of what at first sight appear two valves, 
but each of which is formed of two pieces, the upper 
ones sharp and longer, and the lower pair blunt. The 
upper pair forms the auger that bores a hole in the 
ground, and the lower conducts the eggs into it after it 
is bored *. 
In the Aptera and Arachnida in general there seems 
no remarkable instrument of this kind; but Treviranus 
has described one in spiders for extruding the eggs of a 
singular construction. It is an oval plate lying between 
the external genitals and spinning organs, and is com- 
posed of a number of small screw-shaped cartilages, con- 
nected together in the most wonderful manner. There 
are few organs, he observes, in the animal kingdom 
which for their artificial mechanism can be compared 
with this. Each cartilage inosculates very closely in the 
adjoining one, and all are besides bound together by a 
strong skin‘, 
* De Geer ii. 835. #4. xxviii. f. 20, 21. Pirate XV. Fic. 22. This 
figure was drawn by a friead —the organ seems more exerted than in 
De Geer’s. J cannot make out the little appendage at the end. 
> Prate XVI. Fic. 2, 3. ¢ Reaum. v. 19—. £. ni. f. 3-6. 
* Arachnid, 40. 
