REVIEWS 359 
the acquirement of permanence of originally variable elements, while the 
Neo-Lamarkian school is engaged in accounting for the variability 
itself. 
The laws of evolution as illustrated by the life-history of the 
brachiopoda are fully discussed by the author. The evidence obtained 
from this class of organisms points to the fact that the evolution of 
those characters which mark the differences between separate classes, 
orders, suborders and even families of organisms, has taken place in a 
relatively short period of time; taking as a measure either the rate of 
general progress in the differentiation of organisms, or the length of 
the life period of each particular genus or family. This rapid evolution 
is difficult to account for by any working of natural selection. Two 
factors are at work in the process of evolution which are designated as 
intrinsic and extrinsic evolution. “‘Zu¢rinsic evolution is conceived of 
as normal expansion and differentiation of the organism itself from 
within, and is the expression, in some way, of an intrinsic tendency of 
the particular race of organisms. The other, extrinsic evolution, 
expresses the limitation and selection exerted upon the organism from 
without.” 
Illustrations of the laws of evolution are further drawn from other 
classes of organisms as the Cephalopoda and Vertebrata. From all 
these illustrations it is pointed out that the geological evidence does 
not emphasize the importance of natural selection as a factor in 
evolution. The following paragraphs may be quoted as setting forth 
the views of author. 
“That which has seemed most conspicuous to the latter class of 
observers (students of living organisms) has been the intimate relation- 
ship existing between morphological difference and environmental 
conditions; paleontological facts point to the greater importance of 
the continuous and progressive process of differentiation and speciali- 
zation of structure and function with the passage of geological time. 
Shen facts examine Cams aen show that evolution is rather an 
intrinsic law of organisms, and is to be discovered in the phenomena 
of variation, which appear to be constantly active, rather than in any 
accidental operations dependent upon the conditions of external 
environment. 
‘“‘Eyolution is seen to be a process that is primarily organic; it is 
expressed in the acquirement of new characters in the course of growth 
by living organisms; and we may as reasonably speak of evolution as 
