APPENDIX. 571 
The following passage from that learned work proves that or- 
gan to be really a sperm-reservoir. 
‘“‘ Impregnation in insects appears to take place while the 
eggs pass a reservoir containing the sperm, situated near the 
termination of the oviduct in the vulva. ‘ In dissecting,’ says 
John Hunter, to whom we owe the discovery, ‘ the female 
parts in the silk-moth, I discovered a bag lying on what may 
be called the vagina, or common oviduct, whose mouth or 
opening was external, but it had a canal of communication 
between it and the common oviduct. In dissecting these 
parts before copulation, I found this bag empty; and when I 
dissected them after, I found it full.’ By the most decisive 
experiments, such as covering the ova of the unimpregnated 
moth, after exclusion, with the liquor taken from this bag in 
those which had sexual intercourse, and rendering them fer- 
tile, he demonstrated that this bag was a reservoir for the 
spermatic fluid, to impregnate the eggs as they were ready for 
exclusion, and that coition and impregnation were not simul- 
taneous?.” 
III. 
Since I wrote the account of the disease in flies, which 1 
denominated a kind of plethora’, I observed one fixed to a 
pane of glass in a window, round which was a semicircle of 
what appeared to be merely vapour, whose radius was nearly 
three-fourths of an inch. Taking it for an aqueous fluid that 
had transpired from the dead animal, I paid no further atten- 
tion to it at that time. But observing from day to day that 
the moisture did not evaporate, after two or three months had 
passed I had the curiosity to examine it more closely; and 
* Phil. Trans. 1792. 186. » Philosophy of Zoology, i. 418. 
© See above, p. 202—. 
