DEVELOPMENT OF THE SCALES AND BONES OF FISHES. 
681 
There exists in nearly all the bones of the Pike more or less of cartilage, which, 
whilst it is partly internal, invariably makes its appearance at some portion of the 
external surface of each bone, and especially at the articulating margins. Around 
this cartilage there is developed a film of chondriform bone, which in some cases 
attains a considerable thickness, and which is again invested with layers of membra- 
niform bone, into the direct composition of which no true cartilage structure ever 
enters. 
The relative positions of these two osseous tissues, as they exist in the Pike, will 
be best comprehended by commencing the inquiry with some of the bones which 
are the least complex in their form. The carpals and stylo-hyals will serve this pur- 
pose^. 
Fig. 37 represents a longitudinal section of a carpal bone from a Pike weighing 
about four ounces. It chiefly consists of a cylindrical rod of cartilage, very much di- 
lated at its two extremities. At each of the latter portions (37 a, a) the cartilage-cells 
exhibit the common ichthyal aspect, being arranged in groups, each of which appears 
to be the result of successive divisions of a primary cell ; or rather perhaps of success- 
ive developments of cells within those previously existing, as amongst the vegetable 
Algse, reminding us strongly of the similar groups seen in a Palmella or a Hcemato- 
coccus. At each tumid extremity the cartilage is only invested by a perichondrium; 
towards the centre it becomes much constricted, and its cells assume a new arrange- 
ment. The groups break upand the individualsbecome re-arranged in interrupted rows, 
those of each extremity curving somewhat inwards ; near the centre of the shaft (37 h) 
these cells are globular, turgid, and almost in immediate contact with one another. 
The central point (37 c) is occupied by a congeries of minute spherical calcareous 
granules, which have become so aggregated at the surface of the cartilage as to pro- 
duce a solid calcareous tissue. These granules are obviously chondriform bone-growths 
in an early stage of development, and correspond very closely, both in structure and in 
arrangement, with what exist amongst the cartilaginous Plagiostornes. Besides this 
central production of chondriform bone, a thin cylindrical layer of the same substance 
(37 d, d') invests the exterior of the cartilage as far as the points, fig. 37 e and e'. It con- 
sists of an aggregation of granules, which, though smaller, in other respects resemble 
those of the centre of the organism. They are seen to be developed in the intercellular 
portions of the cartilage, leaving large round open areolae, each of which is occupied 
by a cartilage-cell ; additions to this chondriform bone are made by the production 
of new calcareous granules at its inner surface, within the tissue of the cartilage. 
Investing this combination of cartilage and chondriform bone, we have a second 
osseous cylinder (37 d), of a very different aspect and origin. It is composed of 
numerous parallel superimposed lamellae, many of which may be traced over the 
entire length of the bone, the more external ones being successively longer than those 
* I may observe that throughout this memoir I have followed the definite and philosophical nomenclature of 
Professor Owen, as employed in his beautiful work on the Homologies of the Vertebrate Skeleton. 
