1881.] Comparative Psychology. 31 
lady ” butterfly is pleasantly impressed on meeting with a 
bed of thistles, and attaches her eggs to the leaves. Why 
she should be thus pleasantly affedted on meeting with a 
thistle we can readily understand if we remember that she 
and her ancestors have for unknown ages fed upon this 
plant. That the pupa-state involves complete oblivion of 
all impressions dating from the larval condition is pure 
assumption. But these considerations by no means imply 
that the female butterfly deliberately and consciously selects 
this or the other plant from the formal convidtion that it, 
and it only, will afford a suitable nourishment for the young 
brood. The female blow-fly is in like manner led to lay her 
eggs by a perceptive feeling excited by the smell of putres- 
cible animal matter. How little reason or Divine guidance 
is concerned in the adtion appears from the fadt that she will 
likewise lay her eggs on certain flowers which give off a 
carrion-like odour, when of course the young maggots perish 
from hunger. 
Why, again, do birds always seledt the most suitable 
material for their nests, and in general such as cannot 
readily be distinguished from surrounding objedts ? Not in 
consequence of a deliberate selection, but because the per- 
ception of this material and of no other is in them part and 
parcel of the building impulse. The perception of the empty 
nest or of a single egg is in birds so closely connected with 
the physiological fundtion of the development of eggs that the 
former induces, or at least stimulates, the latter, whilst the 
perception of a sufficient number has the contrary effedt. 
Wild ducks even steal each other’s eggs, and some birds will 
even seat themselves upon the nests of others — a clear proof 
that the sight of eggs awakes in them a desire to hatch, and 
that birds sit because it affords them pleasure. 
The migration of birds likewise requires no unconscious 
clairvoyance for its explanation. Natural seledtion is to some 
extent here concerned. Those individuals which do not 
depart in autumn perish, and the species is perpetuated by 
those only which feel the wandering impulse at the right 
time. Old birds which have already travelled from Europe 
to Africa, and have become accustomed to connedt want or 
abundance with certain states of the atmosphere, are urged 
by conceptive feelings to take their departure. All the phe- 
nomena of autumn suggests to them migration just as the 
sight of eggs arouses the impulse to hatch. Their senses 
and their intelligence are sufficiently developed to instrudl 
them in what quarter to seek for warmth. In finding their 
way they have advantages which we men often forget. 
