VIII] THE SEGMENTATION OF THE EGG 603 



four re-entrant angles, that is to say a figure representing the five 

 sides of a hexagon, and one cell is in touch with seven others, 

 I have found no examples among pubhshed figures of segmenting 

 It is obvious enough, without more ado, that these phenomena 

 2 2 



Fig. 254. (a) Egg oi Echinus; (6) do. oi Nereis, under pressure. 

 After Driesch. 



a b 



Fig. 255. (a) Eg^of frog, under pressure (after Roux); 

 (6) probable actual arrangement. 



are in the strictest and completest way common to both plants and 

 animals, in which respect they tally with, and further extend, the 

 fundamental conclusions laid down by Schwann wellnigh a hundred 

 years ago, in his Mikroskopische Untersuthungen iiher die Ueberein- 

 stimmung in der Struktur und dem Wachsthwn der Thiere und 

 Pflanzen*. 



But now that we have seen how a certain limited number of 



types of eight-celled segmentation (or of arrangements of eight 



cell-partitions) appear and reappear here and there throughout the 



whole world of organisms, there still remains the very important 



* Berlin, 1839; Sydenham Society, 1847. 



