90 CRYSTALLINE LENS. 
form the primary structure of the crystallie lens, and no 
fibres can be detected in the early stage, and since the more 
fully-developed lens of the foetal pig exhibited many fibres and 
fewer round cells, and at the same time cells which became 
elongated into fibres, we cannot but regard the fibres gene- 
rally as elongated cells. It is true that a cell-membrane 
cannot be distinguished on the fibres, nor can it be distinctly 
recognized on the round cells. If, however, the arguments 
above cited rendered its existence in the round cells certain, 
they must avail equally in the case of the fibres. Nuclei 
are also frequently found upon the fibres of the foetal pig. 
Some of the fibres are flat. I have, also, several times ob- 
served an arrangement of the nuclei in rows; but I do not 
know what signification to attach to the fact. A blending of 
several cells to form a fibre may also possibly occur; but I 
have no observations decisive of the pomt. In fishes also, 
in a young pike for instance, the elongation of the cells into 
fibres may often be very distinctly seen. 
Brewster found that many fibres of the crystalline lens, espe- 
cially in fishes, exhibit the remarkable peculiarity of having 
their margins serrated. PI. I, fig. 18, represents such a fibre 
taken from the innermost lamina of the lens of a pike. The 
fibres are flat, and their sharp margins furnished with long 
teeth, which are so disposed, that two neighbouring fibres lock 
into each other by them. We have here an instance of perfect 
analogy to a form of vegetable cells, which is delineated in fig. 
14: it is an epidermal cell of a species of grass. It is very 
much elongated, quite flat, and furnished on the sides with 
teeth precisely similar to those of the fibres of the lens, which, 
in like manner, fit in between the denticulations of the con- 
tiguous cells. The fibre-cells of the crystalline lens which are 
delineated, have somewhat longer teeth in comparison with the 
breadth of the cell; they represent, however, some of the most 
strongly denticulated fibres. On pursuing the examination 
from the external towards the internal lamine, the same lens 
will be found to present all possible stages of transition in this 
serration, from the smooth or only minutely-notched cells, 
to such as are strongly denticulated like those in the figure. 
This striking accordance of so remarkable a form of animal 
structure with a similar modification of vegetable cells, is a 
