418 PHILOSOPHY OF ZOOLOGY. 



male, can produce an egg. The conjunction of the sexe?, 

 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 furnished 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 in 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 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 va- 

 gina, 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 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 

 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 weiv not 

 simultaneous. It has not been determined whether the 

 same arrangement prevails in a,ll 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- 



* Phi). Trans. 1792, p, 18G 



