366 



January 21, 1836. 

 RODERICK IMPEY MURCHJSON, Esq., V.P., in the Chair. 



George Biddell Airy, Esq., M.A., A.R. ; George Budd, B.A. 

 and M.A. ; the Rev. Humphrey Lloyd, M.A. ; the Rev. William 

 Taylor; and Charles Wheatstone, Esq.; were elected Fellows of 

 the Society. 



Sir David Brewster's paper, entitled, " On the Anatomical and 

 Optical Structure of the Crystalline Lenses of Animals, being the 

 continuation of the paper published in the Philosophical Transac- 

 tions for 1833," was resumed and concluded. 



The author has examined the structure of the crystalline lens of 

 the eye of a great variety of animals belonging to each of the four 

 classes of Vertebrata; and has communicated in this paper a de- 

 tailed account of his observations, arranged according as they re- 

 late to structures more and more complex. In a former paper, 

 published in the Philosophical Transactions for 1833, the lens of the 

 Cod fish was taken as the type of the simplest of these structures, in 

 as much as all the fibres of which it is composed converge, like the 

 meridians of a globe, to two opposite points, or poles, of a spheroid 

 or lenticular solid ; both of which poles are situated in the axis of 

 vision. The structure which ranks next in respect of simplicity is 

 that exhibited in the Salmon, among fishes ; in the Gecko, among 

 reptiles j and in the Hare, among Mammalia. It presents at each pole 

 two septa placed in one continuous line, in different points of which 

 all the fibres proceeding from the one surface to the other have their 

 origin and termination. A structure somewhat more complex is 

 met with in the lenses of most of the Mammalia, and is particularly 

 exemplified in the lion, the tiger, the horse, and the ox. Three 

 septa occur at each pole in the form of diverging lines inclined to 

 one another at angles of 120°. The next degree of complexity is 

 presented in the lens of the whale, the seal, and the bear, which 

 contain, instead of three, four septa on each side, placed at right 

 angles to each other in the form of a cross. In some specimens of 

 lenses of whales and seals the author observed two septa from each 

 pole, forming one continuous line, from each of the extremities of 

 which proceeded two others, which were at right angles relatively to 

 one another : so that there were in all five on each surface. The 

 most complex structure is that of the lens of the elephant, which 

 exhibits three primary septa diverging at equal angles from the pole, 

 and at their extremities bifurcating into two additional septa, which 

 are inclined to each other at angles of 60°, these latter being the 

 real septa, to which the fibrous radiations are principally related. 

 In some lenses of the elephant the author found the three septa 

 immediately proceeding from the poles exceedingly short, and ap- 

 proaching to evanescence ; so that he has no doubt that occasion- 

 ally they may be found to have disappeared, and that the other six 

 septa will then all diverge from the poles, like the radii of a hexagon, 

 at angles of 60°. 



In all the preceding cases, where the arrangement of the fibres 

 is symmetrical on the two sides, the septa on the opposite surface 



