CRYSTALLINE LENS. 8H 



They have much the same course as the others, that is, they 

 form arches from the anterior towards the posterior surface. 

 They do not, however, reach the axis either in front or behind, 

 but the fibrous zone is thickest in the middle, gradually dimi- 

 nishes towards the anterior and posterior surfaces of the lens, 

 and terminates altogether without the fibres meeting anywhere 

 in front, or reaching the axis. No laminated structure can 

 be perceived in the zone ; but the fibres may he readily insu- 

 lated throughout its entire breadth. When the ends of these 

 fibres are examined, they are found to be either simply rounded 

 off, or to terminate in a small round dilatation, or to pass over 

 into larger globules (cells) ; or, on the contrary, it may be more 

 correctly expressed by saying, that the larger globules or cells 

 become elongated to these fibres (see pi. I, fig. 12). The 

 transition from cells to fibres may either be very gradual or 

 somewhat sudden ; but even in the latter case, the contour of 

 the cell passes immediately over into that of the fibre, so that 

 the latter is not merely affixed to the globule, but is a true 

 continuation of it. Now, these cells which become elongated 

 into fibres, perfectly accord with other neighbouring cells which 

 are as yet quite round ; and these again accord with the cells 

 forming the greater portion of the lens in the embryo chick. 

 They are round, extremely pale, smooth, transparent cells of 

 very various size (see pi. I, fig. 10). Some have a very beau- 

 tiful, sharply-defined, oval nucleus, which, in most instances, is 

 not flattened, and which lies upon their wall, and encloses one 

 or two nucleoli. Some cells are scarcely larger than the nu- 

 cleus which they contain, fig. 10, b, for example. Some of 

 these enclose young cells (fig. 10, d), and as they may be ob- 

 served to flatten against the wall of the parent -cell, there would 

 seem to be no question about the existence of a special cell- 

 membrane for the latter, and thus the true cellular nature of 

 these globules appears indubitable. The presence of the nu- 

 cleus, and the fact of the outlines of the cells being too sharply 

 defined for mere shadows, would, however, have been sufficient 

 to render their cellular character probable. The very distinct 

 nucleoli contained in the nuclei, which are not flattened, lie 

 upon the inner surface of the wall and not in the centre, as 

 represented in fig. 11. 



Since, then, the round cells, as we have seen in the chick. 



