662 
PROFESSOR WILLIAMSON ON THE STRUCTURE AND 
On returning to the latter preparation, we at once see that the square membranous 
compartments (19 yand 20 d) are really the concentric lines (18 c) cut across, whilst 
the intervening- septa (20 e) correspond with the concentric calcareous plates (18 d). 
In the former, some large bundles of fibres are seen to proceed horizontally inwards ; 
and we shall subsequently find that the dark lines traversing the vertical calcareous 
septa in the same direction, are produced by prolongations of these fibres which pass 
through the septa without becoming calcified. I have already shown that the large 
central area (19 e) is the result of the unilateral direction taken by the section 
(fig. 18 a a'), which here traverses one of the membranous compartments (19/') longitu- 
dinallij instead of transversely , as is the case with those right and left of it. The 
numerous small orifices at fig. 19 A: are those of the kosmine canals, 18 A and '2Qh, 
which are here traversed at right angles, owing to the same cause. 
Below these concentric compartments we find a solid calcareous layer, 19 / and 20/', 
forming a conical, six-sided dome, the margins of which approximate towards the 
inferior surface of the scale as they approach its periphery. It is perforated by 
kosmine canals, 19 i' and 20^, resembling those existing in the upper tissues, but 
here they are neither so numerous nor so extensively developed, being more confined 
to the marginal portions. 
Beneath the dome-shaped septum there are several calcareous laminae, 19 c and 20 h, 
extending from side to side, the upper ones being necessarily smaller than those 
which are inferior. At their margins they are continuous with the substance of the 
conical dome. Like the vertical septa, these laminae are also penetrated by bundles 
of uncalcified fibres, 20 i. 
It is impossible to study the distribution of these calcareous tissues without being 
struck with the way in which they are adapted to the purpose of strengthening the 
scale, and by maintaining its slightly arched form, enabling it to resist a large amount 
of external pressure. The dynamic principle displayed in the arrangement of the 
horizontal laminae (19 c), strengthening the dome {\9 d), is precisely the one acted 
upon in the construction of the light iron roofs of modern railway stations ; whilst 
the small compartments with which the dome is surmounted, vividly remind us of 
the “cells” which constitute so important a dynamical element in the construction 
of those recent triumphs of engineering art, — the tubular bridges. Surely the engineer 
might study some of nature’s contrivances for resisting pressure with great advantage, 
even though embodied in so insignificant a structure as a fish’s scale. 
Before proceeding to a more minute examination of the fibrous membranes, I 
would direct attention to a modification of these calcareous structures, as seen in 
the abdominal scales of Ostracion cornutus, for examples of which I am again in- 
debted to Sir Philip Egerton. 
The dermal plates of this species are constructed on the same general plan as those 
just described ; but they exhibit a little variety in the arrangement of their details. 
There only exist two or three of the vertical calcareous septa, seen to be so mime- 
