WIUJAM KEITH BROOKS — CONKIJN 



necessary to assume that the germ is as complicated as the 

 adult, since under certain conditions the descendants of a single 

 cell may become modified in several divergent directions. He 

 maintains that Darwin's hypothesis may be so simplified that 

 the gemmules may be few in number, simple in their properties, 

 and not infinitely small. Nevertheless, this theory requires us 

 to believe that the egg of one of the higher animals is complex 

 beyond our powers of conception. It is interesting to note 

 that he discusses (p. 131) those cases in which a hybrid re- 

 sembles one parent or the other, but not both (what we now 

 know as Mendelian inheritance), and he suggests a possible 

 explanation by means of his hypothesis of pangenesis. In 

 similar manner he discusses saltatory evolution (pp. 157, 

 296), and agrees with Huxley, Galton, and Mivart that nature 

 does make considerable jumps (mutations), especially in the 

 case of domesticated animals and cultivated plants. As in- 

 stances of this kind he cites the sudden appearance of spike- 

 horned bucks in the species Cervus vir ginianns , the ancon ram, 

 the japanned peacock, and several similar cases among plants, 

 and he "points out that our view of the cause of variation im- 

 plies that any particular change should in itself be a fruitful 

 source of still greater modifications, so that as soon as a tend- 

 ency to vary becomes established it will continue to increase 

 until an equilibrium is again established by the natural selec- 

 tion of those modifications which are adapted to the environ- 

 ment." 



With regard to the determination of sex, he concludes that 

 "sex is not determined by any constant law; that in certain 

 animals and plants the sex is determined by certain conditions, 

 while in other groups it is determined by quite different condi- 

 tions" (p. 317). These are only a few of the subjects of 

 present-day interest which are discussed in this book, and 

 which he attempts to explain by his modified hypothesis of 

 pangenesis, and although this hypothesis has no defenders at 

 present, the book is still stimulating and suggestive. 



It is interesting, and to many of his followers saddening, to 

 see how far Brooks wandered in later life from the study 

 of the physical phenomena of heredity and variation into 

 metaphysical speculation. In two papers written in the last 



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