126 FORMATION OF SHELLS OF ANIMALS, ETC., 
comparison of these parts in bones of different classes of 
animals. The bone of fish, presenting the greatest 
irregularity in structure, is well adapted for the demon- 
stration of this fact ; and I know of no part better than the 
caudal fin-bone of the anchovy, simply cleared of the 
surrounding structures, and examined in water or glyce- 
rine. In some parts of this bone irregular spaces occur, 
of a form inclining to that of an ordinary lacune, and 
with canaliculi branching out from them ; but they directly 
communicate with, and are of about the same size as, a 
small Haversian canal; so that, partaking equally of the 
character of both, it is not possible to determine whether 
they ought to be considered as belonging to the former or 
to the latter named parts. In other parts of the same 
bone minute spaces are seen, presenting fusiform enlarge- 
ments, but prolonged at each end into a filiform 
structure. Some passages of a similar kind have no 
distinct enlargement, but continue nearly of the same size 
until they inosculate with canaliculi from other lacunee of a 
more characteristic form. In such instances the dis- 
tinction between canaliculi and lacune is so obscure that 
one cannot be distinguished from the other. These facts 
show that such spaces and interstices are of no vital 
importance, and agree with the general inference 
that they merely serve to give lghtness to the 
denser parts of bone, and thus their office in the 
osseous tissue seems to be analogous to that of the 
meshes or areolz in other tissues of mferior density, such 
as hgaments, tendons, &c. which are composed only of 
fibrous material, which itself in a modified form enters 
also largely into the composition of the hardest parts of 
the densest bones. The correctness of this view is cor- 
roborated by the structure of the lamine spiralis, as just 
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