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of capsules which I could not doubt were entire, and where 

 their intrusion was impossible ; and because I have^ as I 

 believe, been able to trace the convohition of the fibrous tissue 

 from the epithelial cells through intermediate phases. A 

 normal lens-fibre, which all allow is the final phase of a 

 capsular epithelial cell, differs hardly less from its initial 

 phase than do some of the elements of these fibre-nucleated 

 webs. The posterior half of the capsule has not any ^ithelial 

 lining, but its inner surface frequently exhibits polyhedral 

 marks, which have been mistaken for an epithelium. They 

 really express the hexahedral oblique cross-sections of the 

 swollen jjosterior ends of the lens-fibres. 



The tissue composing the lens itself consists in greatest 

 part of long, flat, ribbon-like fibres. These have two wide 

 surfaces, and four narrow ones meeting on two thin bevelled 

 edges, which give to their cross-sections a hexahedral figure. 

 The fibres are reaUy long tubes filled with the protein sub- 

 stance to which chemists have given the name globulin. 

 TVTien the fibres are broken across, it escapes in the form 

 of globules from their ends. It often accumulates in large 

 masses between the layers of fibres in lenses which have been 

 artificially hardened with chromic acid. 



A nucleus is present in all the superficial fibres, near the 

 edge of the lens ; but the deeper fibres are more sparingly 

 nucleated. The fibres cohere very closely by their flat sur- 

 faces, and still more intimately by their bevelled edges. These 

 latter in some vertebrates are serrated, which renders their 

 union still more secure. This serration is very coarse in fish 

 and in some chelonia ; much finer in snakes ; so fine in frogs 

 that the edges of the fibres appear only as slightly frayed ; it 

 is absent from the human lens. 



The other constituent of the lens is the interstitial tissue, 

 a formless substance present in very minute quantity in the 

 axis of the lens, and in those extensions of the axis called the 

 central or axial planes. In young persons the refractive 

 index of this substance agrees with that of the fibrous tissue ; 

 hence their lenses are free from the internal reflexions which 

 the lenses of elderly persons exhibit, and which give these an 

 opalescence which an incautious observer may readily mistake 

 for a cataractous opacity. The axis in the simplest form of 

 lens, as that of some fish and of amphibia, is a streak or line 

 of this interstitial substance traversing the centre of the lens. 

 The lens-fibres are grouped around it in the manner of the 

 meridian lines on a globe, the inner fibres progressively 

 shortening towards the centre of the lens. In other fish, and 

 in the porpoise and rabbit amongst mammals, the axial streak 



