248 Edmund B. PFilson. 



earlier results formulated for these types seemed wholly subver- 

 sive of the mosaic-principle and of the nearly related one of ger- 

 minal prelocalization. In the sea-urchin egg, the first in which 

 an isolated blastomere was shown to be capable of producing a 

 complete dwarf larva, the experiments seemed at first to show 

 that the blastomeres are composed of indifferent material, so that, 

 to cite an early statement of Driesch's, "Durch die Theilung bei 

 der Furchung vollig gleichwerthige, zu allem fahige (indiffer- 

 ente) Stiicke geschaffen werden" ('92.2, p. 36), forming a ma- 

 terial "welches man in beliebiger Weise, wie einen Haufen Kug- 

 eln durch einander werfen kann, ohne dass seine normale Ent- 

 wicklungsfahigkeit darunter im mindesten leidet" {op. cit. p. 

 25). Despite the fact that Driesch early recognized that the 

 cytoplasm of this egg is not isotropic, he considered that his ex- 

 periments definitely overthrew His's principle of "Organbildende 

 Keimbezirke," or at least deprived it of all casual significance in 

 the echinoderm egg ('92.1, p. 178, '93, p. 243). Specification of 

 the early cleavage cells was denied ('92.2, p. 22), as was also the 

 principle of mosaic development as applied to this egg (1. c, p. 

 36). Again, in the paper of 1899, on "Die Localization mor- 

 phogenetischer Vorgange," where Driesch's theory of vitalism is 

 first definitely formulated, the ground is taken that "Darin nam- 

 lich, das jeder beliebige Eitheil, sowie das Eiganze in beliebiger 

 Verlagerung eine ganze Larve llefern, also jede 'Organization,' 

 die postulierte Vorbedingung zum Eintritt lokalisirten speci- 

 fischen Geschehens iiberhaupt, nach Storung, regulatorisch wieder 

 herzustellen vermag, kommt zum Ausdruck, das eben die 'Struck- 

 tur' des Eies nicht aus mannigfach-verschiedenen Elementen in 

 irgendwie typisch-specifischer Lagerung aufgebaut sein konne, die 

 etwa zu den spateren Differenzierungen in irgend einer Bezie- 

 hung stiinde" {op. cit., p. 43). It is hardly necessary to point 

 out how greatly all this has been changed by Boveri's discovery 

 of the fact that the sea-urchin egg does in point of fact contain 

 "mannigfach-verschiedene Elemente" disposed in a "typisch- 

 specifischer Lagerung," which are proved by the experiments of 

 both Boveri and Driesch to stand in definite relation to the sub- 

 sequent process of cleavage and differentiation. The relation of 



