1901] MICROSCOPICAL JOURNAL. 197 
the former conditions of life upon the earth. The scales 
of fishes, unlike the scales of most reptiles, are not. epi- 
dermal appendages—7. e., they do not grow upon the 
skin, like hairs, nails, or hoofs, but are produced within 
the substance of the skin, and are covered throughout 
their extent with a layer of it. A cursory glance will 
show that the scales figured in books are of two kinds, 
those having a comb-like appearance at one end, and oth- 
ers without this characteristic. The former are known as 
“ctenoid,” and the latter as “cycloid.’’ In the ctenoid the 
comb-like end is the free end, the scolloped part being 
imbedded in the skin. The scales are so arranged in re- 
lation to each other that the water glides from the edge 
of the one on to the middle of the next. The scalesove - 
’ lap in the direction from head to tail of the fish. Two 
objects are attained. The fish swims with the least pos- 
sible amount of friction, and the underlying skin is shield- . 
ed from the constant maceration to which it would be 
subject if the water were perpetually soaking between. 
Unlike the armonur-plated “placoid’’ and sheeny-coated 
“sanoid” fishes of the geologic seas, which still have their 
representatives in our modern waters, the scales here de- 
scribed are delicateand flexible. ‘Ctenoid’ and “cycloid”’ 
differ in appearance; but whether comb-like or rounded 
the structure is very much the same. An examination 
will show anumber of consecutive lines which correspond 
approximately to the shape of the scale. A little carefui 
‘focussing reveals also that the scale,however thin, is thick- 
er at the centre and thin towards the edges. In some 
scales the concentric lines are continuous across the fur- 
rows formed by the deep radiating lines of the upper half: 
In the flounder and the perch they do not meet, but are 
broken by a line of transparent matter which appears also 
to line the whole scale on its underside. The explana- 
tion seems to be that the scale grows by the addition of 
a new layer to its underside, slightly larger than the last, 
