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most of them being much larger than the fibre-cells, and some as large as the largest adipose cells. They can very rarely be seen without the aid of the most favorable light, but when, under such circumstances, the observer has once detected one of them, and become familiar with the degree of its transparency, they may be recognized in great numbers. They have a distinct nucleus attached to the internal surface of their wall, containing one or two nucleoli. The nucleus always attracts attention first; the cell surrounding it is either quite transparent, and void of granules, or has granulous contents, and this granulous deposit is first formed in the neighbourhood of the nucleus, the remaining portion of the contents being still transparent. (See the figure.) Gradually, the entire contents appear to become granulous. These cells are distinguished from the fibre-cells of areolar tissue by the circumstance of their becoming much larger than the latter, and their not being elongated into fibres, and from the adipose cells, in that they do not contain fat. I have found them in areolar tissue taken from the bottom of the orbit, and from the neck of a feetal pig, but do not know whether they occur in the areolar tissue of all parts of the body; nor can I determine their signification. They might be regarded as cellular spaces which had been produced by the distension of the areolar tissue with air. In such case, they must communicate with one another in the course of their further development. But this appears to me to be somewhat improbable ; and those spaces may be merely artificial productions. I should rather regard the cells in question as a modification of the adipose cells. For since, according to Gurlt, the ordinary adipose cells in the adult may contain mere watery fluid, one may also conceive the cells destined to the formation of fat becoming completely developed, without that formation actually taking place within them. There are, indeed, adipose cells which contain fat even in the earliest stage of their development, but that is no reason why the formation should not take place at a much later period in other cells. The granulous deposit in many of them might be regarded as the transitional step to the formation of fat. The cellular tissue of the foetus differs in its chemical con- stitution from that of the adult, since we cannot obtain any