CHAP. II. SIGHT OF BIRDS. 55 



which should be their principal guide. The swiftness 

 with which a hird can fly, may indicate the extent of 

 its reach of vision ; not, however, absolutely, but rela- 

 tively. A bird, whose flight is quick, direct, and sus- 

 tained, may certainly be supposed to see further than 

 another which moves more slowly and obliquely. It 

 is, indeed, obvious that, if nature had ever produced 

 birds with short sight and rapid wing, they must have 

 soon perished from this contrariety of qualities one of 

 which not only hinders the exercise of the other, but 

 exposes the individual to an infinite number of risks. 

 From all this we may perceive that the birds whose 

 flight is shortest and slowest, are also those whose power 

 of vision is the least extended." It is not a little re- 

 markable, that birds form the only class of vertebrated 

 animals which do not present us with a single example 

 of the visual organs existing in a merely rudimentary 

 state. Among quadrupeds, we have the mole, the Or- 

 nithorynchus, or ducksbill, and several of the Glircs, 

 or mouse tribe, with the mere rudiments of eyes. The 

 same partial blindness occurs among fishes in the apodal 

 order, as also in the class of Amphibia and of reptiles ; 

 but nothing analogous to these instances is found in 

 the class of AVES. We conclude, therefore, that the 

 sense of sight is more developed in this, than in any 

 other of the vertebrated circle. 



(71.) Sight, however, is but one of the five senses ; 

 and although so highly developed in birds, these animals 

 do not exhibit a corresponding degree of perfection in 

 the others. That of smell, indeed, must be very acute 

 among the toucan family, and is probably equally so in 

 the vultures ; for the first have to scent out the nests 

 and eggs of birds, upon the last of which they chiefly 

 feed ; while the latter are well known to be guided by 

 the smell of decomposing animal substances from a vast 

 distance, notwithstanding some plausible theories to the 

 contrary : but, in other respects, the smell of the ma- 

 jority of birds seems to be very imperfect, because 

 then great power of vision and locomotion renders it 



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