DEVELOPMENT OF THE SCALES AND BONES OF FISHES. 
663 
I'ous in fig. 19, and a corresponding difference exists in the number of the subjacent 
horizontal laminse. The superficial portion also presents some points of difference. 
Fig. 22 represents a vertical section of the upper textures, as they appear at the ex- 
treme margin of the scale. The concentric lamellae (22 a) are here seen to be largely 
developed and perforated by even a still greater profusion of minute tubes, the orifices 
of which open at the external surface. I’hese tubes give off numerous branches, 
and an immense number of minute recurved, falcate twigs, which are peculiar and 
characteristic. 
The extraordinary development of this superficial system of tubes is compensated 
for by the absence of the secondary twigs fringing the large canals (22 b), which 
enter from the margins of the scale. The principal trunks recur, and are distributed 
in the same way as before; but the small branches which gave them their character 
of kosmine tubes are wanting; they are thus reduced to the condition of mere Ha- 
versian canals. The terminal twigs of the superior series of tubes begin to appear 
almost immediately above, instead of at a distance from them, and thus traverse a 
part of the space which, in the previous example, was occupied by the tubuli branch- 
ing from these horizontal canals. The subjacent calcareous portions resemble those 
already described. 
The singular structure of the membranous tissues of the decalcified scale of 
O. cornutu.s affords a good illustration of that of the preceding species, and of the 
group in general. Fig. 23 represents the centre of a vertical section of a scale sub- 
sequent to its immersion in weak hydrochloric acid. From this specimen we perceive 
that the distinctions seen in the scale prior to decalcification, partly exist in the 
membrane also. The upper tissue (fig. 23 a) still exhibits its wavy lamellee, and 
traces of the vertical tubuli. The horizontal series of canals (23 b) are also conspi- 
cuous, communicating with the large vertical prolongations (23 c') which proceed 
downwards towards the lower surface of the scale. The two lines (23 dd) sloping 
away right and left in the downward direction correspond with the calcified dome- 
shaped layer (i) of fig. 19. The lower portions of the decalcified scale consist of 
numerous thick laminae, which are horizontal in the centre (23 e), but turn upwards 
as they successively reach the line 23 d. Thus we see that the dome-shaped layer 
divides the membranous as well as the calcareous laminae into two series ; those which 
are superior to it being vertical to, and those which are inferior being parallel with 
its surface. The horizontal and vertical portions are, however, continuations of each 
other. 
Each lamina, as seen at 23 e, consists of two sets of fibres ; when a horizontal 
section is made near the centre of the scale, those belonging to one of these series 
are observed to form its chief substance; they are very minute, and arranged hori- 
zontally in parallel lines, being only deflected here and there so as to allow bundles 
of the second series to pass between them in a more or less vertical direction from one 
lamina to another. The latter series are especially obvious in the central and upper 
4 Q 2 
