SOME NEW BOOKS. 



The Agency of External Influences in Development, 



Aeussere Einfluesse als Entwicklungsreize. Von August Weismann, 

 Professor in Freiburg i. Br. Jena ; Verlag von Gustav Fischer, 1S94. 



The Effect of External Influences on Development. The Romanes Lecture, 

 1894. By August Weismann, M.D., Ph.D., D.C.L., Professor in the University 

 of Freiburg in Breisgau, with annotations by the Author. London ; Henry 

 Frowde, Amen Corner, E.C. Oxford: Clarendon Press Depository, 1894. 

 Price 2S. 



We have before us Dr. Weismann's lecture, published by the 

 Clarendon Press, and purchased by ourselves, and the German edition 

 sent us with the usual courtesy of the German publisher. The 

 preface in the two editions is slightly different. Both contain a kindly 

 and appreciative reference to the late Professor Romanes. The 

 German preface calls attention to an additional note added at the 

 end of the German text, and dealing with some of the matter contained 

 in Hertwig's " Preformation or Epigenesis," an account of which 

 has recently been published in Natural Science. 



The German text is the original from which the translation was 

 made by Mr. Gregg Wilson. It certainly serves to show that 

 Professor Weismann is not so oblivious of the agency of external 

 influences in development as Oscar Hertwig implies in his recent 

 criticism. It deals, not with the whole field suggested by the title, 

 but specially with the agency of certain external influences that 

 call into activity varied constituent parts in the process of 

 development. It is, then, in no measure a withdrawal from 

 the preformationist position. It is an argument to show that many 

 external influences that have been supposed to affect the process 

 of development as direct causes in the epigenetic sense, that 

 in fact have been supposed directly to stamp certain characters 

 upon organisms, stamp these characters not directly but by calling 

 into activity latent but existing constituents of the germ-plasm. As 

 was explained in his book, Weismann believes that in the germ-plasm 

 that gives rise to the organism there are present many sets of parts, 

 each of them capable of producing the whole organism. In the 

 actual development, when the germ-plasm is disintegrated into the 

 separate parts or determinants which control the production of 

 the separate variable parts of the animal, for each separate indepen- 

 dently variable part there are many determinants present, and hence a 

 struggle ensues between these as to which of them shall acquire the 

 mastery and guide the growth of the organ in question. When the 

 environment seems to have an important direct effect, Weismann 

 believes that it is, so to speak, merely interposing in the struggle 

 between the determinants, egging on some of them that otherwise 



