THE SCALES IN SOME TELEOSTEAN FISH. 57 
As development proceeds, the basal portions of all the 
scalelets fuse to form a continuous plate, except at the lines 
of intermission. The spines appear to fuse laterally with 
their neighbours, thus giving rise to the excentric markings 
which have been seen to be in reality projecting ridges. 
Comparison with the scales of the cod show certain points 
of marked difference. In the latter individual scalelets remain 
distinct in certain species—for example, in G. virens and 
G. callarias ; though in G. minutus, as has been said, 
there is a considerable amount of lateral fusion; while in 
all species there is an entire fusion, with a total absence 
of spines in the region of the centrum. The same influ- 
ences seem to have been at work in the clupeoid scale, and 
to have carried their results still further. The condition 
found in the centrum of the cycloid scale is identical with that 
seen in the posterior uncovered portion of the clupeoid, 
while in the anterior part fusion has taken place to a greater 
extent, the basal portions of the scalelets fusing throughout to 
form a continuous sheet (except at the lines of intermission), 
while a lateral fusion involving the spines has given rise to 
the continuous excentric ridges. 
There is one point of marked difference in comparison with 
the scales of such a form as G.virens. In the latter the 
appearance of excentric lamination is due to an imbrication of 
the scalelets, the spines having more or less disappeared, 
whereas in the clupeoids there is no such imbrication, the 
excentric markings being produced by the spinous portions of 
the scalelets. 
What have been the determining causes of these differences 
in the various scales, or for the retention and disappearance 
of the spines in the anterior and posterior portions respectively 
of the individual clupeoid scale, I am unable to say. The 
disappearance on the exposed portions of the latter cannot be 
due to friction, or it would equally have affected the exposed 
part of the cycloid scale. I am inclined to think that the 
retention of the spines in the covered areas may have the 
effect of retaining the scales in position, since in the 
