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2f kikd's-eye views. 



To commence by saying that all birds have eyes, migfit 

 appear at first sight to be superfluous. Yet this statement 

 expresses one of the chai-acters of the cliiss Aves; for it is 

 not applicable, without some qualification, to any other class 

 of Vertebrates. Some representatives of each of the other 

 classes either have no eyes at all or else veiy rudimentary 

 ones. There are blind fishes and blind reptiles ; and there 

 are mammals at least "as blind as a mole." Among birds ^ 

 the "wingless" species of New Zealand (Apteryx) are said 

 to have the smallest eyes of all, and also to want one of the 

 most characteristic structures of the avian eye-type, — the 

 marsupium, a peculiar organ inside the eye, of which we 

 shall learn something before we have finished our "Views." 



We will examine first the accessory structures of a bird's 

 eye, — those that surround and defend it, produce its move- 

 ments, and keep it in working order ; and then we will look 

 at the more exquisite mechanism within. 



If we hold a dying bird in our hands, we observe that just 

 as the last convulsive shiver agitates its frame, the eyes close 

 by the uprising of the lower lid. In the primitive theatres 

 of classic days, the curtain was lowered from the top to dis- 

 close the stage, and drawn up when the act was over ; now 

 these movements are reversed. Birds follow the classic 

 usage, when the curtain rises upon the last scene of their 

 life. Here at the outset is one difierence between the eye 

 of a bird and that of a mammal ; and diflerences will mul- 

 tiply as we proceed. 



The movements of the upper lid, in almost all birds, are 

 much more restricted than those of the lower. There are 

 few exceptions to this rule, and these chiefly furnished by 

 the nocturnal raptores (Owls, Strigidm), and certain fissi- 

 rostrcs {Capri7nulgidce, e. g., Whippoorwill, Night-hawk). 

 Both lids are composed of common skin externally, a mem- 

 brane internally (the palpebral part of the conjunctiva, to be 

 noticed presently), with a layer of fibrous tissue interposed 

 for i^rcater streno^th. Besides these tissues, the lower lid 



