1878.] The Senses of the Lower Animals. 293 
colour by small birds generally is indisputable. Everyone 
must have observed with varied feelings the discrimination 
with which they select the “ sunny side ” of a pear, a plum, 
or a peach. It is also an established fadt that they will 
attack the red currant in preference to the white variety, 
though the latter is much the sweeter of the two. Many 
observers during the last few years have pointed out 
how the yellow crocus is torn to pieces by sparrows and 
other birds, while the white and other varieties are unmo- 
lested. We are reminded of a curious fadt which we do not 
know whether to ascribe to imperfedt perception or to 
animal stupidity. A bullfinch which we kept in our cham- 
bers long ago was seized every evening with the desire to 
go to roost upon a line painted upon the wall about twenty 
inches from the ground. Time after time the poor fellow 
flew up only to be disappointed before he would consent to 
perch upon something tangible, and the next day he resumed 
his vain attempts. 
The phenomena of mimetism or of protedtive resem* 
blances, of which so many signal instances have been 
pointed out by Messrs. Wallace, Bates, and Belt, neces- 
sarily involve a tolerably nice discrimination of colour. 
Brilliantly-coloured serpents are often especially dangerous, 
and are hence mimicked protectively by innocent species. 
But unless such colouration were distinguished by mammals 
and birds, they would neither avoid the former nor be de- 
terred from attacking the latter. 
Caterpillars displaying gay and striking hues are generally 
offensive in smell and taste, or even poisonous, and are 
hence avoided by birds. But if the latter were incapable of 
recognising colours, such a conspicuous dress would not 
deter them from seizing the unsavoury or unwholesome 
morsel. 
But the sight of some at least of the lower animals may 
very possibly differ from our own in a manner not indicated 
above. The human retina is sensitive only to a portion of 
the sun’s rays. Thus, if we allow a pencil of sunlight to 
fall into a darkened room through a slit in the shutter and 
to pass through a prism, we have the well-known spedtrum, 
all the seven primary colours of which are visible to the 
eye. But above and below this spedtrum, where our sight 
finds nothing but darkness, there are solar rays whose pre- 
sence may be demonstrated by appropriate chemical and 
physical means. Now, if the retina of any creature is 
sensitive to the whole or a portion of these, to us, dark rays 
it will be able to see where we should find total obscurity. 
