It is easy to see which elements of the tissues of this and the preceding class correspond. There the whole tissue consisted of cells, closely crowded together, and the intercellular substance was almost nil. Here we find the like arrangement only in the lowest stage of development of the most simple cartilages. In such as are more highly developed, those of all the mammalia for example, the cells lie surrounded by a larger quantity of intercellular substance, which forms the proper cartilaginous substance ; but the cell-walls contribute only very slightly, or not at all, to its formation. The proper firm substance of these higher cartilages, therefore, has its analogy in the former class, only in the minimum of cytoblastema by which the cells are connected, while, on the other hand, it corresponds with that which, in the first class, was the fluid, wherein the isolated cells were formed. The cartilage-cells in this class, however, correspond precisely to the epithelium-cells, the feather-cells, &c. &c., in the preceding one, and the blood-corpuscles, mucus-corpuscles, &c. in the first class.
We have not found any new changes in the form of the cells in this class. Most of them were angular, somewhat approaching the circular form; and stellated cells, so far at least as we may be permitted to regard the osseous corpuscles as such, were also frequently met with. (See pp. 29, 30.) Some cells, which were remarkably elongated, were observed near to the surface of several cartilages, in which situation they are known as greatly elongated cartilage-corpuscles; still, however, this appearance is never presented by the cells of this class in so remarkable a degree as it is by those of the crystalline lens in the previous one. The fibro-cartilages, on the other hand, form the immediate transition from this to the following class, for in them a bundle of fibres seems to be formed out of each cartilage-corpuscle, a process which we shall consider more minutely when treating of cellular (areolar) tissue in the next class.
We have observed the formation of cells around the previously-existing nucleus, and their progressive growth, going on in this class in a similar manner to that exhibited in the preceding, and the true cartilage-cells were also seen to form around a cytoblast which lay external to the cells already
