VIIl] 



THE SEGMENTATION OF THE EGG 



605 



again peculiar, and is probably rare, but it is included under the 

 cases considered on p. 491, in which the cells are not in complete 

 fluid contact but are separated by Httle 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. 256, 1 and 2, 



4 5 6 



Fig. 256. Various modes of grouping of eight cells, at the dorsal or 

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



we have the arrangements corresponding to I and g, and in 3 and 4 to c 

 in our table on p. 598. One thing stands out as very certain indeed: 

 that the elementary diagram of the frog's segmenting egg given in 

 textbooks of embryology — in which the cells are depicted as 

 uniformly symmetrical and more or less quadrangular bodies — is 

 entirely inaccurate and grossly misleading*. 



* Cf. Rauber, Neue Grundlegungen z. K.Mer Zelle, Morphol. Jahrb. viii, p. 273, 

 1883 : " leh betone noch, dass unter meinen Figuren diejenige gar nicht enthalten ist, 



welche zum Typus der Batrachierfurchung gehorig am meisten bekannt ist Es 



haben so ausgezeichnete Beobachter sie als vorhanden besehrieben, dass es mir 

 nicht einfallen kann, sie liberhaupt nicht anzuerkennen." See also 0. Hertwig, 

 Ueber den Werth d. erste Furchungszelle fiir die Organbildung des Embryo, 

 Arch. f. A7iat. XLin, 1893; here 0. Hertwig maintains that there is no such thing 

 as "cellular homology." 



