360 THE LENS, BY PROFESSOR BABUCHIN. 



The transition of the epithelial cells into the fibres of the lens 

 does not occur in this way in all animals. A modification 

 which Heinrich Miiller found to occur in Birds and in the 

 Chamseleon, and which I and Sernoff observed in many scaly 

 Reptiles, is that, in opposition to what takes place in other 

 animals, the flat epithelial cells become higher, and not far 

 distant from the anterior pole assume the characters of 

 columnar cells, then gradually elongate as far as to the plane of 

 the setyuator, and from thence onwards shorten, though they 

 never again present the character of flat epithelial cells. These 

 constitute the vertically placed radial fibres of the lens, which 

 had previously been noticed by Treviranus and Briicke in the 

 lens of the Bird. All these fibres, or, more correctly speaking, 

 all these elongated cells, appear more or less regularly hexa- 

 gonal on section ; their peripheric extremity is broader than 

 their central, and is not hexagonal, but rounded on section. 

 At this end there is usually a single round or oval sharply 

 defined nucleus. In the anterior half of the lens these cells 

 adhere firmly by their anterior extremities to the inner sur- 

 face of the capsule of. the lens; but in the posterior half, as 

 Sernoff has shown in Birds, they become separated almost 

 immediately behind the sequator from the inner surface of 

 the capsule, so that around the whole lens a flat circular 

 canal is formed, which is filled with a structureless mass. 

 Sernoff and I have met with an exactly similar canal to 

 this of Birds in the embryoes of many Mammals and of Man, 

 situated behind the point of transition of the anterior epithe- 

 lium into the fibres of the lens. In Man it exists even for some 

 time after birth, and in Birds it is persistent throughout life. 



Whilst, as already stated, the radial cells become shorter at 

 the posterior part of the lens, they change their direction, and 

 from being radially arranged become obliquely placed, and thus 

 are gradually converted into meridianally placed lenticular 

 fibres, just as in Mammals. 



We shall now proceed to consider in what mode the fibres of 

 the lens participate in the formation of the posterior thick 

 layers of the nucleus, and consequently of the most important 

 part of the whole structure. The process is essentially the 

 same in all Vertebrata, Flat fibres unite to form curved 



