APPENDIX. 



NOTICES OF BOOKS. 



The Biological Prohleni of To-day. By Dr. Oscar Hertwig. Authorised 

 translation by P. Chalmers Mitchell, M.A., with an Introduction 

 by the Translator and a Glossary of the technical terms. Lon- 

 don : William Heinemann, i8g6. 



Dr. Hertwig is well known for his brilliant powers, both as an 

 original investigator and as a critical exponent of the bearings of Biolo- 

 gical research. It is hardly necessary then to say that his book will be 

 read with keen interest by all who are attracted by the newer results of 

 Biological speculation. 



And the value of the translation is not a little enhanced by Mr. 

 Mitchell's extremely clear Introduction, which will enable many to 

 appreciate the points of the argument who might otherwise be dis- 

 couraged by lack of familiarity with the subject treated of. 



The object of the book is to explain the issues involved in the 

 controversies raging respectively around Evolution and Epigenesis. 

 Dr. Hertwig adopts the latter position, and he deals some very heavy 

 blows at the foundations which underlie the doctrines of Weisniann 

 and of others who have more or less openly declared themselves as on 

 the side of the Evolutionists or Preformationists. 



One by one the author deals with the principles regarded as essential 

 by his opponents ; he discusses the consequences of the assumption of 

 discrete material particles as associated with the existence of as many 

 different hereditary qualities, and he points out how impossible it is to 

 reconcile these assumptions with the facts of regeneration and of hetero- 

 morphosis without calling in the aid of an elaborate series of accessory 

 hypotheses. 



Having finished with the destructive criticisms levelled at the 

 germplasm theory. Dr. Hertwig devotes the second part of the volume 

 to the outlining of his own views as to the ways and means of organisa- 

 tion and development. To use his own words : " I start from the con- 

 " ception that the ovum is an organism that multiples by division into 

 " numerous organisms like itself. I shall explain the gradual, progressive 

 " organisation of the whole organism as due to the influences upon each 

 " other of those numerous elementary organisms in each stage of the 

 " development. I cannot regard the development of any creature as a 

 " mosaic work. I hold that all the parts develop in connection with each 

 " other, the development of each part always being dependent upon the 

 " development of the whole." These statements are supported by con- 

 siderations drawn from organic form, from observed correlation of 

 development, from the modifying influence exerted by the environment, 



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