152 ANNUAL OF SCIENTIFIC DISCOVERY. 



wander very far, as the grouse and partridge, have much less difference in 

 the two portions of the retina; while in those birds whose flight is far and 

 prolonged, as the crow, rook, swan, goose, and duck, the entrance of the 

 nerve is very nearly to the centre of the ball. So in reptiles. In the turtle, 

 who only requires to see immediately before and under him, the outer and 

 tipper portions of the retina are very much the larger. In the more active 

 alligator, frog, toad, and chameleon, while the upper portion maintains its 

 size, the outer and inner parts are more nearly equal. In those creatures 

 whose habitation is for the most part under ground, as the shrew and the 

 mole, the eyes arc so small as to have led Magendic to assert that the mole is 

 without the organs altogether, which is not the fact, for I have found all the 

 essentials of an eye, even true retinal elements, optic nerve, and a well-devel- 

 oped choroid. Yet the organ is so minute, and concealed by the skin and 

 hair, as probably only enables the creature to discern the light, which is all 

 that it requires; for, living underground, where it seeks its prey, it obviously 

 must depend upon the acutcness of other senses than of sight for its living. 

 Though in the individual there is usually some proportion between the size 

 of the eye and the body, taking different classes and genera, the size of the 

 animal is very little guide to that of the eye, the proportions between the two 

 being determined by other considerations than that of the bulk alone of the 

 creature; for though, as a whole, the eye in fish bears a larger proportion to 

 the whole body than it does in other divisions of the animal kingdom, and 

 the eyes of birds arc, as a class, much larger than those of mammalia or 

 reptiles, yet amongst the different genera of all these classes there are very 

 great differences, determined, apparently, by the following considerations, 

 amongst others not so obvious. When the creature lives in feeble light, yet 

 moves actively about, and is guided in its locomotion by the sense of sight, 

 as in nocturnal birds and animals and fish, the eye is very large, apparently 

 to take in a large quantity of the feeble light; on the contrary, where the 

 creature is guided in its movements by other senses, then the eye is very 

 small, as in the bat, the mole, the shrew, and the eel. Where vision pene- 

 trates to a long distance, and where the eye enjoys great power of overcom- 

 ing the aberration of parallax, the eye is large, as in rapacious birds. When 

 the brain and intellect are more developed, the size of the eye diminishes, 

 and the two eyes become more parallel, as in man and the higher mammalia. 

 Where animals are feeble, timid, have but little defensive power, and are 

 preyed upon, the eye is usually very large, as in the hai-e, the. conies, the 

 whole deer tribe, and many of the other ruminants. Where the animal is 

 not predacious, and the size and strength are such as to protect it from being 

 preyed upon, the eyes are commonly small, as in the whale and the elephant : 

 in the latter the eye is even smaller than it is in the horse, and scarcely larger 



than in the eagle. 



KALEIDOSCOPE TOP. 



Under the above name a beautiful philosophical toy has lately been ex- 

 hibited to the London Society of Arts. It is a top, with a flat disk of wood, 

 and a spindle in its centre, by which it is set in motion with a string. On 

 the upper surface of the disk cards of various colors and shapes are placed, 

 and held by pins, and the top is set in motion. This produces pleasing 

 effects, as a blue and yellow card exhibits a green color, a red and blue card 

 a purple, and a red and yellow card an orange color. By taking a black 

 card pierced with holes, and held steady above the rotating colored cards, 



