330 THEORIES OF INHERITANCE AND DEVELOPMENT 



when all these admissions are made, and when the conserving 

 action of natural selection is in the fullest degree recognized, we can- 

 not close our eyes to two facts : first, that we are utterly ignorant of 

 the manner in which the idioplasm of the germ-cell can so respond, 

 to the play of physical forces upon it as to call forth an adaptive 

 variation ; and second, that the study of the cell has on the whole 

 seemed to widen rather than to narrow the enormous gap that sepa- 

 rates even the lowest forms of life from the inorganic world. 



I am well aware that to many such a conclusion may appear reac- 

 tionary or even to involve a renunciation of what has been regarded 

 as the ultimate aim of biology. In reply to such a criticism I can 

 only express my conviction that the magnitude of the problem of 

 development, whether ontogenetic or phylogenetic, has been under- 

 estimated ; and that the progress of science is retarded rather than 

 advanced by a premature attack upon its ultimate problems. Yet 

 the splendid achievements of cell-research in the past twenty years 

 stand as the promise of its possibilities for the future, and we need 

 set no limit to its advance. To Schleiden and Schwann the present 

 standpoint of the cell-theory might well have seemed unattainable. 

 We cannot foretell its future triumphs, nor can we repress the hope 

 that step by step the way may yet be opened to an understanding of 

 inheritance and development. 



LITERATURE. IX 



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schaften: Sitz.-Ber. d. Ges. f. Morph. unci P/iys. hi Miinchen, V. 1889. See 



iX'i.o ArcJi. f. Eiitiviii . 1895. 

 Brooks, W. K.— The Law of Heredity. Ballimorc, 1883. 



Driesch, H. — Analytische Theorie der organischen Entwicklung. Leipzig, 1894. 

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von Vorgangen in der tierischen Ontogenese : BioL Centralb., XIV., XV. 



1894-95. 

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 Id. — iJber den Werth der ersten Fiu-chungszellen fur die Organbildung des 



Embryo: Arch. mik. Anat., XIA\. 1893. 

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 His, W. — Unsere Korperform und das physiologische Problem ihrer Entstehung. 



Leipzig, 1874. 

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Wiirzburg, \?>()i . II. Organbildung und Wachsthum. IVnrzdurg, iSg2. 

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