418_ PHILOSOPHY OF ZOOLOGY. 
male, can produce an egg. The conjunction of the sexes, 
however, is necessary for the impregnation of the egg, and 
the effect is produced previous to the exclusion. 
In many kinds of fishes and reptiles, the yolks, after be- 
ing furmshed with their glaire, are ejected from the body 
of the female, and the impregnating fluid of the male is 
afterwards poured over them. Impregnation can be effect- 
ed readily im such cases, by the artificial application of the 
spermatic fluid. 
Impregnation in insects appears to take place while 
the eggs pass a reservoir containing the sperm, situ- 
ated near the termination of the oviduct in the vul- 
va. ‘* In dissecting,” says JouN 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 va- 
gima, 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 expe- 
riments, such as covermg the ova of the unimpregnated 
moth, after exclusion, with the liquor taken from this bag 
in those which had sexual intercourse, and rendering them 
fertile, 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 
simultaneous. It has not been determined whether the 
same arrangement prevails in all insects. This is a very 
near approach to the external impregnation of the ova, as it 
takes place in many fishes and reptiles. 
After the ovum has been impregnated and ejected, it re- 
* Phil. Trans. 1792, p, 186 
