VIIl] 



THE SEGMENTATION OF THE EGG 



381 



Of these six illustrations, two are exceptional. In Fig. 168, 5, 

 we 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 equili- 

 brium. 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 



4 — 5 



Fig. 168. Various modes of grouping of eight cells, at the dorsal or 

 epiblastic pole of the frog's egg. (After Rauber.) 



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 "touching-up," to exhibit their mathematical 

 regularity. It will easily be recognised that in Fig. 168, 1 and 2, 

 we have the arrangements corresponding 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 



angular intersection ; and he was accordingly disposed to look upon the configura- 

 tion represented above in Fig. 168, 6, as the most typical or most primitive. 



