VISION. 497 



led Sir David Brewster to the farther discovery 

 of the curious mode in which, (as is represented 

 in Fig. 432,) the fibres are locked together at 

 their edges by a series of teeth, resembling 

 those of rack- work. He found the number of 

 teeth in each fibre to be 12,500; and as the 

 whole lens contains about 5,000,000 fibres, the 

 total number of these minute teeth amounts to 

 62,500,000,000.* 



Some fishes, which frequent the depths of the 

 ocean, being found at between three and four 

 hundred fathoms below the surface, to which it 

 is impossible that any sensible quantity of the 

 light of day can penetrate, have, like nocturnal 

 quadrupeds, very large eyes.t In a few spe- 

 cies, which dwell in the muddy banks of rivers, 

 as the CcEcilia, and 3Inrcena cceca, or blind eel, 

 the eyes are quite rudimental, and often nearly 

 imperceptible ; and in the Gastrobrcmckus, De 

 Blainville states that it is impossible, even by 

 the most careful dissection, to discover the least 

 trace of eyes. 



Reptiles, being destined to reside in air as 



* As far as his observations have extended, this denticulated 

 structure exists in the lenses of all kindsof fishes, and likewise in 

 those of birds. He has also met with it in two species of Lizards, 

 and in the Ornithorhyncus ; but he has not been able to find it 

 in any of the Mammalia, not even in the Cetacea. (Phil. Trans, 

 for 1833, p. 323.) 



t See " Observations sur les Poissons recueillis dans un ^'oy- 

 age aux lies Baleares et Pythiuses. Par M. Delaroche." 



VOL. II. K K 



