88 CRYSTALLINE LENS. 
mode of life has been considered as generally resembling that 
of vegetables. We shall find the latter to be the correct view, 
and the singularity of the mode of its nutrition disappears 
altogether, when we become acquainted with the fact, that the 
growth of the organized tissues resembles that of vegetables. 
The general statement, that the lens has the vitality of a vege- 
table, does not, however, express much, unless the relation of 
its elementary structure to the cells of plants be proved. The 
lens is known to be composed of concentric layers, made up of 
characteristic fibres, which, not to go into details, may be said 
to pursue a general course from the anterior to the posterior 
surface. 
In order to become acquainted with the relation which these 
fibres bear to the elementary cells of organic tissues, we must 
trace their development in the foetus. When the lens of a 
chick is examined after eight days’ incubation of the egg, no 
fibres are to be found; but it is composed of round, extremely 
pale, and transparent smooth cells. Some contain the charac- 
teristic cell-nucleus, in others it cannot be detected ; and there 
are also many nuclei without surrounding cells. Some larger 
cells may be observed in the chick at a more advanced period, 
which contain in their interior one or two smaller ones (see 
pl. I, fig. 10, d, from a foetal pig), and from the manner in which 
these cells become flattened against the wall of the parent-cell, 
as well as from the presence of the nucleus in other cells, we 
may conclude, that these pale globules are actually cells, al- 
though a cell-membrane be not distinctly recognizable. Wer- 
neck, who first observed them, likewise calls them cells. 
The following conditions of the crystalline lens may be ob- 
sorved in Mammalia. In a foetal pig, three and a half imches in 
length, the greater part of the fibres of the lens is already 
formed ; a portion, however, is still incomplete; and there are 
many round cells awaiting their transformation. The perfected 
fibres form a sphere in the centre of the lens; but there is no 
laminated structure as yet perceptible in it. The fibres may 
readily be separated from each other, and proceed in an arched 
form from the anterior towards the posterior side of the lens. 
This sphere, composed of the perfected fibres, becomes sur- 
rounded, in the circumference of the lens, with a thick and 
broad zone of fibres, which are as yet imperfectly developed. 
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