Mr. R. J. Lee on the Sense of 8ight in Birds. 143 



size and coefficient of refraction of the lens, the extent and character 

 of the retina, and particularly those differences of minute structure 

 which have relation to susceptibility to light, by which the night- 

 flying birds are distinguished from the day-flyers. Nor does the in- 

 quiry into the eff'ects of domestication upon the sight appear less 

 interesting. 



It is only to point out the various ways in which we may deal with 

 this subject that I have mentioned these diff'erent lines of research, 

 and in order that it may be understood that I have not overlooked 

 their importance. It is to one particular property of the eye that 

 my own observations have beeil chiefly directed, namely the power 

 of accommodation for distance ; and I shall endeavour to show that 

 in birds great range of vision depends upon the development and 

 character of the ciliary muscle, to which all are agreed that the power 

 of adjustment is to be attributed. 



It is chiefly, then, a comparison of the ciliary muscle in different 

 birds to which I invite attention, assuming the perfection of the sight 

 to depend on this power of accommodation, and that again on the 

 character of the muscle. Let me first mention the general opinion 

 entertained by those who are best acquainted with the habits of 

 that class of birds which astonish us by the rapidity and duration 

 of their flights, namely the pigeons, in regard to the means by which 

 they accomplish them. In his interesting work on this subject Mr. 

 Tegetmeier gives his reasons for concluding that " homing," as it is 

 termed in the Antwerp pigeon, is not the result of " instinct," but 

 of " observation." These pigeons require to be trained stage by 

 stage, or they are certain to be lost. The l)est of them refuse to fly 

 in a fog or in the dark. They crave in new localities some known 

 landmark ; and hence their gradually increasing gyrations, until 

 having descried some familiar object, they recollect their route and 

 fly straight ahead. The objection that no pigeon can possibly see 

 for two hundred miles ahead is met by the details of aeronautic ex- 

 perience. Mr. Glaisher, half a mile aloft in air, could embrace in 

 his " bird's-eye view" the course of the Thames from the Nore to 

 Richmond ; and Mr. Wheelwright, though puzzled to account for 

 the flying pigeons " homing" across seas (as from London to Ant- 

 werp), which can off'er no landmark, is disposed to attribute their 

 power of doing so to their habit of soaring round, circling, and 

 beating about until, sooner or later, they can descry their familiar 

 guide-posts. 



My own observations entirely support Mr. Tegetmeier's conclu- 

 sions. This part of ray subject is one of general interest ; and I 

 trust that I shall be pardoned for attempting to alleviate the tedious- 

 ness of anatomical details by this digression. 



It must clearly be understood that perfection of sight for very near 

 objects is as important as very extensive range, and that the chief 

 function of the ciliary muscle is to adjust the sight for the former 

 rather than for the latter. When the eye is at rest (that is to say, 

 when the muscle is relaxed) vision of very distant objects is permitted ; 

 and it is when the distance is diminished to a very few inches, and 



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