NoveMBER 8, 1918] 
evolutionary impulse ”he conceives as mainly 
determined by the innate properties of the 
germinal substance, 7%. e., by “chromatin po- 
tentiality ” (p. 231). This potentiality deter- 
mines the rate of appearance and the character 
of new variations independently of natural 
selection; for example, paleontology shows 
that the slowly breeding race of elephants, 
on which selection might be expected to act 
slowly, have evolved much more rapidly than 
the frequently breeding rodents (p. 271). 
Everything depends upon the “invisible pre- 
dispositions and tendencies in the ancestral 
heredity chromatin” (p. 242). There is, how- 
ever, no evidence in paleontology of an in- 
ternal extraphysical directive principle or en- 
telechy; on the other hand, environmental con- 
ditions appear to exert a direct modifying in- 
fluence, not attributable to selection, upon the 
evolving organism, but the nature of this in- 
fluence remains obscure (pp. 248-244). That 
the germinal material possesses a power of 
“adaptive response” to the environment is in- 
dicated (e. g.,) by the evolution of teeth (p. 
257). 
In general, therefore, the author refers the 
evolution of the various metazoén stocks pri- 
marily to germinal variations, 7. e., more spe- 
cifically, to variations of an orthogenetic or 
definitely directed kind in the “ heredity chro- 
matin.” The evolution of visible bodily form 
and function is to be regarded as essentially 
the external sign and symbol of the invisible 
evolution of the heredity chromatin (p. 151). 
This “chromatin evolution” has its distine- 
tive peculiarities; it is not “ experimental” or 
hap-hazard but tends to be continuous in one 
direction toward adaptive ends (p. 146); evo- 
lutionary progress is thus not dependent either 
upon mutations or upon fortuitous variations 
which are held to a definite course only through 
the agency of natural selection. In a certain 
sense the author supports the Weismannian 
conception that the evolutionary factors act 
primarily upon the “ germ-plasm,” rather than 
upon the “soma”; he recognizes, however, 
that somatic modifications may secondarily in- 
fluence the germ; and he appears to favor a 
kind of qualified Lamarckianism (p. 244); he 
SCIENCE 
473 
suggests that possibly bodily changes may in- 
fluence the germ through the intermediary of 
hormones (pp. 278 seg.). He insists, however, 
that the factors determining germinal evolu- 
tion are still for the most part unknown (cf. 
pp. 28, 151). 
The problem of the causes of germinal varia- 
tion is essentially a physiological one. Every- 
where in the book the author emphasizes the 
difference between the somatic and the germ- 
inal material, and it seems to the reviewer that 
this distinction is too sharply drawn. Cer- 
tainly it can not be maintained in the case 
of the lowest organisms, e. g., the bacteria or 
the ultramicroscopic forms of life, in which 
nevertheless heredity and variation are as 
truly manifested as in the highest. Such 
forms multiply or proliferate in a manner 
which is specific or true to type, but which may 
be influenced in definite directions by changes 
(e. g., chemical) in the surroundings; and the 
same is undoubtedly true of all growing or 
developing regions in multicellular organisms, 
including the special germinal material (egg- 
cell and embryo) at the different stages of its 
development. Any form of organic growth 
implies the property of incorporating and as- 
similating, 7. e., transforming specifically, food 
and other materials taken from the surround- 
ings; this property constitutes in fact the es- 
sential or distinctive feature of vital activity; 
it is common to all forms of living matter and 
heredity is one of its expressions. Hence the 
germ-cell can not be regarded as fundamentally 
different in its physiological constitution and 
properties from other cells or tissues of the 
organism. It is true that in higher animals 
the fertilized egg-cell has special powers of 
development not normally exhibited by other 
regions after isolation; but in many lower 
forms almost any detached portion of sufficient 
size may act as a germ, 7. e., may proliferate 
under favorable conditions and give rise to a 
complete organism. The appearance of a 
sharp distinction between soma and germ in 
higher organisms is itself a product of evolu- 
tion; it represents a differentiation which does 
not exist in the lowest forms of life. Weis- 
mann’s distinction is based upon the fact that 
