Faculties of Vision in Birds 91 



accounted for their thus congregating and appearing 

 suddenly from immense distances to their soaring high in 

 the air for the purpose of looking out for food. 



It is said in St. Matthew, as the received translation 

 gives it, that, ' ' where the carcase is, there will the eagles 

 be gathered together," and in Job it is said " Where the 

 slain is, there is she." Now, it is well known that the 

 eagle does not feed on carrion, and it has been proved by 

 experiment that it will not touch it unless pressed by 

 hunger (Selby). Yet Professor Paxton contends with St. 

 Jerome that the eagle is certainly meant in the text, and 

 quotes, after Bochart, the Arabian historian, Damir, who 

 asserts that the eagle can discover a carcase at a distance 

 of four hundred parasangs, with this singularity, that if 

 he finds parts of it have been previously eaten by the 

 osprey he will not touch the leavings of his inferior. This 

 circumstance makes rather against Dr. Paxton's opinion, 

 supposing the authority Damir to be good. In conse- 

 quence of this apparent discrepai cy between facts and 

 the text, St. Chrysostom proposed to read ' ' vultures " 

 for " eagles " in the passages both in Matthew and Job 

 (Chrysos. Horn., xlix.). Aldrovaid, it would appear, 

 has given the only judicious solution of the difficulty by 

 referring to a very common Oriental species (Gypaclus 

 barbatus, Storr), which was remarked by Aristotle to be 

 similar in form to the eagle, but had more the habits of the 

 vulture. 



Besides the nictitating membrane in the eye of birds, 

 which is not altogether peculiar to them, there is another 

 singular part of the organ whose use has not hitherto been 

 clearly ascertained. It is called by the French Academi- 

 cians the Purse [Marsupium) and the Comb (Pecten 

 plicatum). It arises in the back of the eye, and, proceed- 

 ing apparently through a slit in the retina, it passes 

 obliquely into the vitreous humour, where it terminates, 

 reaching in some species to the capsule of the lens. 

 Numerous blood-vessels run in the folds of the membranes 

 which compose it, and the black pigment by which it is 

 covered suggests the idea that it is chiefly destined to 

 absorb the rays of light when they are too strong or 



