272 THE AMERICAN NATURALIST.  [VOuL. XXXII. 
divisions of the foam the continuous element varies its viscosity by 
some unexplained changes within its finer structure, so that from a 
fluid state it may almost instantly become viscid to varying degrees, 
even to a semblance of true solidity. It is subject to displacement 
by contraction activity which may be rhythmically organized or may 
be of a filose nature. ... 
“The continuous substance is at any given moment the physio- 
logically active element of protoplasmic masses.... Upon its re- 
. sponse in character of its powers, or properties, to specific and 
general environment depend all the physiological phenomena char- 
acterizing areas, masses, or organisms as such. It is homogeneous 
throughout all areas alike, as to its intrinsic powers and characters, 
but not as to the specific, or habitual, expression of these, which 
varies with its chemical or physical contacts.” 
The discontinuous elements, or protoplasmic inclusions, are hetero- 
geneous in character and form the “ specific environment ” of the 
living substance. This is regarded by the author as the most im- 
portant source of the stimulus which determines the course of 
protoplasmic activity. 
The author’s position in regard to the cell theory recalls the view 
of Wolff that the cell is not a fundamental unit, but merely an in- 
cidental expression of the vital activities of the continuous living 
substance. Although not expressed in these terms, she appears to 
agree with Driesch and Hertwig in regarding the differentiation of 
an area as a function of its position. 
This is enough to give an idea of the scope and tenor of the 
book, which the reader, if not discouraged by a style which at times 
renders comprehension difficult, will find to contain much that is 
suggestive and interesting. 
Isolation and Physiological Selection.!— Professor C. Lloyd 
Morgan has earned the gratitude of all biologists by completing 
the work so well begun by Romanes. The third and last vol- 
ume of the Darwin and after Darwin was issued late in 1897. O 
this the first two chapters and the last were in type at the time 
of the death of the author. The material in the remaining three 
chapters has been selected and arranged by Professor Morgan. 
The first two chapters are devoted to a general discussion of 
the principle of isolation. ‘‘Equalled in its importance by the 
1G. J. Romanes, Darwin and after Darwin; III, Post-Darwinian Ques- 
tions: Isolation and Physiological Selection. Chicago, Open Court Pub. Co., 1897- 
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