56 THE BIOLOGICAL PROBLEM OF TO-DA Y 



it follows that the id of germplasm itself pos- 

 sesses a bilateral structure, and that it also divides 

 so as to ofive rise to the determinants of the risrht 



o o 



and left halves of the body. This illustration may 

 be taken as a further proof of our view of the 

 constant architecture of the germplasm.' 



Roux 1 has based his mosaic theory upon ex- 

 periments upon frogs' eggs. According to the 

 theory, the first two segmentation spheres contain 

 not only all the formative material for the right 

 and left halves of the embryo respectively, but also 

 the differentiating and elaborating forces for these, 

 so that on the destruction of one cell, the other 

 can give rise only to one lateral half of the embryo 

 (hemiembryo lateralis). Roux, therefore, considers 

 that by the first cleavage the nuclear material is 



1 Roux tried to give experimental evidence in favour of his 

 mosaic theory in a treatise On the Artificial Productions of Half- 

 Embryos "by the Destruction of one of the first two Cleavage-Cells, 

 and on the Reconstruction of the Lost Parts. Vircliows Archiv., 

 vol. cxiv., 1888. Roux defends his mosaic theory against Driesch 

 and myself in (1) Ueber das entwicklungsmechanische Vermogen 

 jeder der beiden ersten Furchungszellen des Eies. Verhandl. der 

 Anat. Grcsdlsch. der 6 tol Vcrsamml. in Wien, 1892. (2) Ueber 

 Mosaikarbeit und neuere Entwicklungshypothesen. Anatomische 

 Hefte von Merkel und Bonnet (1893). Also in Biol. CcntralUatt 

 (1893) ; in the Anatom. Anzeiger (1893), and in the treatise Die 

 Methoden zur Erzeugung halbcr Froschcmlriionen und sum Nachweis 

 der Beziehung der erstcnFurchujirjschenen des Froscheies zur Mcd'nt ,><- 

 bene des Embryo. Anatom. Anzeiger. (1894) ; Nos. 8 and 9. 



If, as would appear from the last treatise, Roux would avoid 

 being reckoned with evolutionists, he must abandon his mosaic 

 theory, and this he has not done. I think in the present essay, 

 on theoretical and experimental grounds I have vshown the un- 

 tenability of Roux's mosaic theory. 



