370 THE LENS, BY PROFESSOR BABUCHIN. 



same reagents ; so that in Fishes, for example, the nucleus 

 remains transparent, hard, and difficult to cut. The cloudiness 

 of the fibres of the lens, and the formation of vacuolre in their 

 interior, are occasioned by the action of reagents which with- 

 draw water from them. 



As regards the origin of the lens, and the mode of develop- 

 ment of its fibres, it is obvious from the above-described direct 

 transition of the anterior epithelial layer of the lens into the 

 posterior fibrous layer, that each fibre of the lens is simply a 

 colossal and greatly elongated epithelial cell, and the history of 

 development shows further that the persistent portions of the 

 body of the lens arise from the epidermoid external layer of 

 the embryo. 



The body of the lens, as has been already stated, is entirely 

 surrounded by a structureless, smooth, and transparent mem- 

 brane. It is only in those cases where the membrane is very 

 thick that in transverse sections of hardened specimens a 

 longitudinal striation can be recognized, favouring the idea of 

 its being laminated. It is not everywhere of equal thickness. 

 In all animals the anterior half, and indeed that portion which 

 is bounded by the line of attachment of the zonule of Zinn, is 

 also thicker than the posterior ; in Man it is about twice as 

 thick. It is thinnest at the posterior pole. The substance of 

 the capsule is tolerably resistant and very elastic ; on section 

 it rapidly rolls up backwards. Several authors have found epi- 

 thelial cells upon the posterior surface of the capsule of the lens, 

 which probably resulted from the circumstance that the inner 

 surface of the anterior capsule has been described as covered 

 with epithelial cells. It would nevertheless be more natural, 

 from the developmental history of the lens, to reverse the 

 matter, to say, namely, that the epithelium which forms the 

 anterior layer and the direct continuation of the posterior, as 

 well as this last itself, is covered by the capsule. It would ap- 

 pear that either the impressions of those posterior extremities 

 of the fibres of the lens which directly abut against the capsule, 

 or the spherical bodies which arise from the breaking-up of 

 these ends, have been taken for epithelial cells. It is extremely 

 difficult to give an account of the development of the capsule. 

 It has been maintained that it is the product of the excretion 



