two cells with three others, and four cells each with four other cells. In type a four cells are each in contact with two, two with four, and two with five. In type f, two are in contact with two, four with three, and one with no less than seven. In all cases the
number of contacts is twenty-six in all; or, in other words, there are thirteen internal partitions, besides the eight peripheral walls. For it is easy to see that, in all cases of n cells with a common external boundary, the number of internal partitions is 2nã₤ãã₤3; or the number of what we call the internal or interfacial contacts is 2(2nã₤ãã₤3). But it would appear that the most stable arrangements are those in which the total number of contacts is most evenly divided, and the least stable are those in which some one cell has, as in type f, a predominant number of contacts. In a well-known series of experiments, Roux has shewn how, by means of oil-drops, various arrangements, or aggregations, of cells can be simulated; and in Fig. 170 I shew a number of Rouxãs figures, and have ascribed them to what seem to be their appropriate ãtypesã among those which we have just been considering; but {384} it will be observed that in these figures of Rouxãs the drops are not always in complete contact, a little air-bubble often keeping them apart at their apical junctions, so that we see the configuration towards which the system is tending rather than that which it has fully attained11. The type which we have called f was found by Roux to be unstable, the large (or apparently large) drop aÿ£¢ã° quickly passing into the centre of the system, and here taking up a position of equiôÙlibôÙrium in which, as usual, three cells meet throughout in a point, at