284 REVIEWS 
The first and fourth factors are what we have usually called the 
environment and the second and third are what we have called heredity. 
According to the conventional view each generation of individuals is the 
result of the co-operation of heredity and environment. ‘There is there- 
fore nothing essentially new about this classification of energy complexes. 
What is really new is the consideration of these factors in terms of energy. 
The inorganic environment is described as so highly adapted for 
organisms that the non-existence of the latter would be well-nigh incon- 
ceivable. In this the author follows closely L. J. Henderson and T. C. 
Chamberlin. The organism is viewed as a system of parts each affecting 
the growth of the others through the instrumentality of ‘chemical mes- 
sengers’”’ or hormones. It is this interaction of energies that gives 
organization to the individual and limits its size as a whole and the 
relative size of its parts. Gradual changes in the activity of one gland 
may alter quantitatively or qualitatively the chemical messengers pro- 
duced by it, and progressive changes in one or many structures may 
result. | 
The heredity-chromatin of Osborn is evidently much like that of 
Morgan and his collaborators, with all of its intricate organization and 
its mechanism for producing new assortments of characters. The treat- 
ment of this energy system is a trifle vague and mystical in that it is 
supposed to go on its evolutionary way in a highly conservative fashion, 
guided only to a very limited extent by other energy complexes. Its 
changes are orderly and from generalized to specialized. Once the 
chromatin becomes specialized it cannot reverse and return to a gen- 
eralized condition. The slow, orderly, self-contained changes of the 
heredity-chromatin are supposed to account for the orthogenetic phe- 
nomena so common in paleontological materials. 
The “life environment”’ is, in a sense, a restatement in energy terms 
of Darwin’s idea of the struggle for supremacy and survival of the fittest, 
but the struggle is inter- rather than intra-specific. Every environmental 
complex is a battleground on which the various groups that have become 
specialized for that particular complex struggle for space to multiply. 
One group may perfect an offensive equipment, another a defensive 
armament. Either type may go to extremes of specialization, so that 
a radical change of environment may find them nonplastic and irrevers- 
ible. This is the author’s explanation of many unaccountable extinc- 
tions. 
Part IL of the book is an application of the principles discussed in 
Part I to the evolution of the various animal groups. It must suffice 
