656 
PROFESSOR WILLIAMSON ON THE STRUCTURE AND 
larger number of open interstices than occur in those scales already described. This 
may partly be owing to the existence of the oblique fibres just referred to. In other 
respects they present no material distinctive feature. Hie layer thins out as we 
approach the margin of the scale. The consolidated tissue first disappears, leaving 
only a layer of minute detached granules, which also soon cease to exist, and the 
marginal portions of the scale consist only of the uppermost and lowest tissues. 
It is the peculiar aspect of the superficial layer which gives the chief interest to 
this curious scale. That portion of its external surface, which, when in situ, is not 
covered over by the antecedent scales, exhibits an aggregation of numerous large 
papillae. The vertical section shows us that these are produced by an extensive de- 
velopment of the upper layer, which is so thick in this species, that it occupies one- 
third of the vertical diameter of the scale. At 13 f, where the preceding scale has 
rested upon it, this tissue is level and smooth ; but at its anterior half its develop- 
ment has produced the large tubercles already referred to. All these various portions 
consist of numerous minute lamellae, arranged in precisely the same way as the 
homologous ones in the scale of the Carp, fig. 9 c. The growth of the tissue has 
evidently been effected by the addition of new lamellae to the upper surface of the 
pre-existing ones. 
These lamellae are perforated by a dense network of anastomosing canals which 
run in every direction ; they are the laigest at the inferior portion of the tissue, where 
it is contiguous to the middle layer, and where they exhibit a marked tendency to 
radiate from tbe centre to the circumference of the scale. These give off numerous 
anastomosing branches, which, as they ascend, diminish in size, and finally open by 
myriads of minute apertures at the external surface. 
This peculiar structure is wholly new to me. It is very different from those den- 
tine-like tissues, to which, in my former memoir, I applied the name of Kosmine. 
The anastomosing tubes have more of the character of the Haversian canals seen in 
the vertical sections of the scale of Megalichthys, only the lamellse whicli they 
penetrate contain none of the lacunae seen in that very beautiful example. They 
bear even a still closer resemblance to the small canals Vv’hich penetrate the true 
osseous dorsal spines of some Siluroid fish, which pass through lamellse crowded with 
lacunae, and are obviously the homologues of the true Haversian canals of the higher 
vertebrata. If the lacunae and their canaliculi were absent from the Siluroid spine, 
the canals in the two examples would correspond as closely as possible ; we shall 
afterwards find that the existence of lacunae is not at all essential to a true osseous 
structure, inasmuch as they are absent from the bones of a large majority of the 
osseous fish; they are an adjunct, but not a necessary one, especially amongst 
fishes; consequently this superficial structure in fig. 13 becomes but a slightly modi- 
fied form of bone. It is equally obvious that it is also the homologue of the cor- 
responding portions of the scales of the Carp, Perch and other Cycloid and Ctenoid 
fish ; only we have here, in addition to the lamellse which it possesses in common 
