This cytoblastema is present in the greatest quantity, and therefore most distinctly demonstrable in the jelly which lies between the chorion and amnion in the foetus of the pig at a somewhat more advanced period, and where it may be rendered very clearly perceptible on the margin of the preparation by colouring it with iodine. It is quite as evident in the cellular tissue of the young tadpole. An indistinct fibrous appearance is sometimes given to it by drawing it asunder; but a fibrous structure must not be inferred from that fact simply, since all tenacious matter assumes that appearance under similar circumstances. Since the number of the corpuscles in the cytoblastema continually increases as development proceeds, it would appear that the cytoblastema must be regarded as the primary formation, so that we may suppose some of it to be first present, and then the corpuscles originate in it; at the same time, however, new cytoblastema is formed, in which new corpuscles are in like manner generated, whilst the formation of those in the previously-existing cytoblastema proceeds simultaneously.
Three kinds of these corpuscles may be distinguished in the mammalian embryo; one, which is developed at an earlier period than the rest, and is found in all the areolar tissue throughout the foetus, and two others, which are formed subsequently, and, as it would seem, do not occur in the areolar tissue of some parts. We shall, therefore, designate the first (which is the only essential kind) proper corpuscles of areolar tissue, or—in accordance with the signification which will shortly be determined for them—fibre-cells of areolar tissue; the second kind are fat-cells; the third form round cells of areolar tissue, the precise signification of which I have not yet been able to make out.
a. Proper corpuscles of areolar tissue, or fibre-cells of areolar tissue. The areolar tissue is not found in the same stage of development in every part of the same foetus. When some of the tissue that has reached about its middle stage of development is removed from the neck of a pig’s foetus, measuring from four to seven inches in length, and examined with the microscope, a quantity of corpuscles of various forms are observed in it. The majority of them, however, appear as they
