xxxii SCIENCE PROGRESS. 



offspring. Hertwig (drawing his own conclusions, which differ from 

 those of Ehrlich) seizes on the latter point and regards it as an example 

 of inheritance of acquired characters, but it would seem that it is possible 

 to explain the facts quite differently. For it is only the female which 

 can transmit the immunity, and even then it only persists for a limited 

 period of the early life of the offspring. Now it is curious that the 

 male has no such power, but it should be remembered that the sperm 

 consists almost entirely of nuclear idioplasmic matter. The egg, on 

 the other hand, contains in addition a relatively enormous mass of non- 

 idioplasmic protoplasm, and it seems likely enough that, just as the 

 protoplasm of the body cells of the parent was rendered immune, so 

 also this bulky substance in the egg possessed a similar property — 

 possibly by virtue of the possession of some antitoxin, or of some ante- 

 cedent of an antitoxin ; and this might readily explain why the immunity 

 soon passed away from the growing offspring. At any rate the evidence 

 for the idioplasm having become itself affected seems extremely pre- 

 carious and of doubtful value. 



This case has been discussed rather fully as it is just one of those 

 instances in which the meaning of " inheritance of acquired characters " 

 may be rendered obscure or ambiguous through not clearly emphasising 

 the difference between an influence affecting the idioplasm and one 

 merely restricted to the non-idioplasmic but still living protoplasm. 



We could wish, indeed, that the theory of Biogenesis itself had been 

 set forth somewhat less vaguely ; it is difficult even to state definitely 

 the main points of the theses embodied in it, but its key-note lies in the 

 idea that the idioplasm is capable of receiving and becoming modified 

 by impressions from without, and that, once such an impress has 

 become one of the characters of the idioplasm of a species, a bias will 

 be manifested which will tend to direct further development along 

 certain definite lines, and thus the course of the future evolution of any 

 o-iven species is profoundly influenced by the steps which, in its ancestral 

 line, it has already traversed. 



There is much in Dr. Hertwig's theory which reminds the reader 

 of Nageli and Lamarck, and, indeed, the author expressly mentions his 

 obligations to these, as well as to many other predecessors, but the 

 orio-inal method of treatment, and the many luminous passages with 

 which it is adorned, will ensure a welcome for the book even at the 

 hands of those who are unable to accept the views which it is its chief 



purpose to express. 



J. B. F. 



Fossil Plants ; for Students of Botany and Geology. Vol. i. By A. C. 

 Seward, M.A., F.G.S., Lecturer in Botany in the University of 

 Cambridge. Pp. 452; with 112 Illustrations. "Cambridge 

 Natural Science Manuals." University Press. 1898. 



The need of a trustworthy and readable manual of Fossil Botany 

 has been urgently felt for some time. Within the last few years 



