SWALLOW TRIBE. 95 
direct opposition to such intense feelings as these ? 
The cause assigned by Dr. Jenner for conduct so 
anomalous is the desire to migrate; and this desire, 
he maintains, is produced by a change in the repro- 
ductive system ; which, in the case of the birds under 
consideration, is supposed to take place prematurely. 
I say is supposed to take place ; for I do not see how 
it is possible to ascertain what individuals will 
desert their progeny before they carry their intention 
into effect ; and after the accomplishment of the act, 
no opportunity of examining the state of their in- 
ternal organization can present itself: this notion, 
therefore, it is pretty obvious, must have originated 
in conjecture. That the sudden departure of the 
Swallow, House-Martin, and Sand-Martin, under 
circumstances so peculiar as those we have been con- 
templating, is occasioned by the desire to migrate, I 
do not dispute; but that this desire results from 
certain changes which occur periodically in the con- 
dition of the reproductive system seems to be quite 
inadmissible. Indeed the undeniable facts that 
every species of the feathered tribes, though subject 
to those changes, is not migratory, and that Snipes, 
Wild Ducks, &c., breed annually, and Woodcocks 
occasionally, in countries where the majority of those 
birds are known to sojourn during the winter only, are 
so totally subversive of Dr. Jenner’s hypothesis, that 
to attempt a more complete refutation of it, in this 
place, would be superfluous. 
