Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/45

OF CARTILAGE, 19 Nuclei, around which no cells have yet commenced to be developed, may be observed in the cytoblastema between the cells in some situations; for example, a and b. These like-wise contain a nucleolus, and are somewhat less than the nucleiin the smaller cells.

The above observations furnish us with a complete representation of the development of cartilage-cells, and show the accordance of that process with the development of vegetable-cells, inasmuch as they exhibit the simultaneous presence in the cytoblastema both of simple nuclei, and of cells containing a nucleus of similar shape and size upon the inner surface of their walls, and which may be observed in all stages of transition, from such as are scarcely larger than the nucleus they contain, to such as are many times its size. Simple nuclei are first present, developed in the cytoblastema. When these have arrived at a certain size, the cell is formed around and closely encompassing them. The cell gradually expands, whilst the nucleus remains lying on a point of the inner surface of its wall. The nucleus, also, increases somewhat in size, but not in proportion to the expansion of the cell. Now these three hypotheses may be assumed from the above facts; either the cell is first developed, and the nucleus subsequently, or both are developed simultaneously, or the nucleus is first developed, and then the cell around it. The first supposition, that the cells are developed earlier than the nuclei, is not possible, since in that case cells would be found at a certain period of development without nuclei. The simultaneous development of a cell, together with its nucleus, as two distinguishable structures, is equally impossible, for then we should observe a stage of development, at which as yet the cell and nucleus had not reached the size of the ordinary nucleus. In order to explain the above observations, we must, therefore, have recourse to the third supposition, viz. that the nucleus is first developed and then the cell around it.

The form of the young cells depends upon the space allotted them for expansion. They are, therefore, either round or angular, according as the neighbouring cells permit of, or limit their regular expansion. Two or more cells are often developed close together in one intercellular space, and thus compress those already formed, and the intercellular substance on the outside of them;