observe that one of the eight cells is surrounded on all sides by the other seven. This is a perfectly natural condition, and represents, like the rest, a phase of partial or conditional equiôÙlibôÙrium. But it is not included in the series we are now considering, which is restricted to the case of eight cells extending outwards to a common boundary. The condition shewn in Fig. 168, 6, is again peculiar, and is probably rare; but it is included under the cases considered on p. 312, in which the cells are not in complete
fluid contact, but are separated by little droplets of extraneous matter; it needs no further comment. But the other four cases are beautiful diagrams of space-partitioning, similar to those we have just been considering, but so exquisitely clear that they need no modification, no ãtouching-up,ã to exhibit their mathôÙeôÙmatôÙiôÙcal regularity. It will easily be recognised that in Fig. 168, 1 and 2, we have the arrangements corôÙreôÙsponôÙding to a and d of our diagram (Fig. 158): but the other two (i.e. 3 and 4) represent other of the thirteen possible arrangements, which are not included in that {382} diagram. It would be a curious and interesting inôÙvesôÙtiôÙgaôÙtion to ascertain, in a large number of frogsã eggs, all at this stage of development, the percentage of cases in which these various arrangements occur, with a view of correlating their frequency with the theoretical conditions (so far as they are known, or can be ascertained) of relative stability. One thing stands out as very certain indeed: that the elementary diagram of the frogãs egg commonly given in text-books of embryology,ãin which the cells are depicted as uniformly symmetrical quadrangular bodies,ãis entirely inaccurate and grossly misleadingÿ£¢10.
We now begin to realise the remarkable fact, which may even appear a startling one to the biologist, that all possible groupings or arrangements whatsoever of eight