27 
on the migration of birds. 
This, I imagine, will admit of an easy explanation. The 
winter birds require nothing here but food and shelter. Our 
summer visitors come for more various and important pur- 
poses. Had they, like the former birds, been endowed with 
a disposition to wander on certain changes of the atmosphere, 
the great design of their migration, as it must have proved 
fatal to the business of incubation and the rearing of their 
young, would have been frustrated. It may be worthy of 
remark, that both the summer and winter migrating birds 
are, on their arrival here, well received by the domestic na- 
tives, and neither create quarrels nor excite fears. The 
redstart builds its nest in the same tree with the titmouse, 
and the redwing feeds peaceably in the same meadow with 
the starling. 
I proceed now to make some observations on another kind 
of migration, directly opposite to the foregoing, namely, the 
return of the spring migrators to their respective homes. 
The great disproportion in numbers between those species 
of birds which quit the country in summer, and those that 
leave it at the autumnal season, has led naturalists to lose 
sight of the early migrators, and to confine their reflections 
on the subject to the late ones only. Hence the common 
observation, that they are all driven off through a failure of 
food, or a cold temperature of the air. But seeing that many 
of them disappear in the summer season, when food is placed 
before them in the greatest plenty, we must seek for some 
other cause. If we examine what is now going forward in 
the animal economy, dissection will point out a change in the 
testes and ovaria, the very opposite to that which took place 
