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ANNIVEESAEY ADDEESS 
who would be triumphant in Scotch or Irish waters will return 
with an empty basket after a visit to a well-whipped stream. But 
however careful fish may be, they are always at a disadvantage 
when tempted by a dry fly, for their eyes as we have seen are 
specially adapted to their habitat, and though they may distinguish 
a stranger from one who regularly supplies them with food, yet 
they seem to detect with difficulty minute differences in an object 
out of water. A friend informs me that the trout in a neigh¬ 
bouring oft-frequented water will not take the welcome natural 
May-fly unless its wings are well raised, owing apparently to the 
fact that the wings of an artificial fly fall on the water after a little 
use. If these fish had a keen vision for floating objects, they would 
recognize the difference between their natural food and its imita¬ 
tion, irrespective of position. 
Amongst the most interesting eyes are those of the Anableps. 
This fish inhabits fresh waters in Central America and the tropical 
parts of South America. It is constantly on the surface, and each 
eye is divided into an upper and lower portion, as if adapted to 
both aerial and aquatic vision. 
The Eyes oe Bieds.— The rapid motion of birds and the ex¬ 
tended horizon which results from their frequent elevated aerial 
position, would lead us to expect adjustments in the eyes of birds 
which are not found in other Yertebrata. 
Sight is the initial means of livelihood to birds. It is essential 
for their safety, if not for the acquisition of their food, that they 
should rapidly focus on their retina the images of external objects, 
even when close to them. We are all familiar with the different 
appearance of striped from unstriped muscle, and we know that 
the duration of the contraction of the latter is the longer of the 
two, and that therefore it is less efficient when quick adjustments 
are required. In our own eyes the muscle which regulates the 
focus of our optic lens is unstriped, but that of birds is striped, 
and hence we may assume that they can change the focus of their 
eyes more rapidly than we can. Moreover, their power of accom¬ 
modation is facilitated by the great mobility of their iris, and by 
muscles which affect the degree of convexity of the cornea and 
the shape of the eyeball. Yet even the adjustment of our lens 
is so quick, that unless our attention has been directed to the 
subject, we think we can focus near and distant objects clearly at 
one time, which is just as impossible with the eye as it is with a 
photographic camera. When travelling by express train we find 
it difficult to observe objects we pass unless they are at some 
distance, yet a bird in rapid flight appears to see its quarry with 
