BLrE SHARK. 
Si 
loss; but as there is some degree of variety in the way in 
which this process takes place in the different species, I will 
enter a little further into the description of it as I have 
observed it in the present one. 
We have already seen that the seat of the tooth-formiiig 
process is in a thick membrane, which covers the jaws on their 
inner surface, and which passes over them externally. This 
membrane is in a condition of perpetual production, and at its 
origin is formed into a series of cells or doublings, in each of 
which the germ of a tooth may be discovered, soft and mem- 
branous, and seemingly nourished from the sides of the sac or 
cell itself. It lies flat along the course of the membrane that 
contains it, with the point directed downward in the lower jaw, 
and towards the roof of the mouth in the upper jaw ; in such 
a manner as that in passing to its final destination, it has to 
go through the third part of a circle, in the course of which 
the upper doubling of the containing cell becomes torn through 
its substance. The enamel of these teeth has no existence at 
first; so that their substance is as soft and flexible as parchment; 
but as their growth proceeds the nourishment from the sides 
of the cell ceases, so that at last it is furnished only from the 
root; and at this stage the circulation of nutriment by the 
vessels appears to be from near the point, along the middle 
line of each tooth, along which the solid firmness they at last 
obtain is clearly to be discerned. 'I" o membrane within which 
these teeth have been formed, is itself constituted of longitudinal 
fibres, of some degree of firmness, with softer cellular membrane 
at the part in which the teeth receive their actual formation; 
and as in the course of nature, the former become more rigid 
from defect of nourishment, they contract in their substance, 
and thus draw the roots of the teeth nearer to the situation 
they are destined to occupy, but still leaving a vacancy which 
can only be supplied by the successive formation of teeth in 
alternate order; the cells of one row being opposite to the 
vacancies of the other, and only pressed closer, because 
the fibrous membrane connecting them has in time admitted 
of a more idgid contraction. In some species of this great 
family, as the Monkfish, ( Sqtiatina angelus,) and many of the 
Ray tribe, the teeth cells are arranged in regular linear suc- 
cession, without the filling up of the vacancies between them; 
