v.] IN THE THEORY OF NATURAL SELECTION. 337 



becomes, ipso facto, adopted to its conditions; and the produc- 

 tion of gemmules ceases, and with it the manifestation of 

 variabiHty itself, for the cells of the organism then derive the 

 whole of their qualities from the egg, and being no longer 

 hybrid, have no tendency to vary. For the same reason the 

 ova themselves will also cease to vary, and the favourable 

 variation will be transmitted from generation to generation in 

 a stereotyped succession, until unfavourable conditions arise, 

 and again lead to a fresh disposition to vary. 



In this way Brooks^ attempts to mediate between Darwin 

 and Lamarck, for he assumes, on the one hand, that external 

 influences render the body or one of its parts variable, while, 

 on the other hand, the nature of the successful variations is 

 determined by natural selection. There is, however, a dif- 

 ference between the views of Brooks and Darwin, although not 

 a fundamental difference. Darwin also holds that the organism 

 becomes variable by the operation of external influences, and 

 he further assumes that changes acquired in this way can be 

 communicated to the germ and transmitted to the offspring. 

 But according to his hypothesis, every part of the organism is 

 continually throwing off gemmules which may be collected in 

 the germ-cells of the animal, while, according to Brooks, this 

 only takes place in those parts which are placed under un- 

 favourable conditions or the function of which is in some wa}- 

 disturbed. In this manner the ingenious author attempts to 

 diminish the incredible number of gemmules which, according 

 to Darwin's theory, must collect in the germ-cells. At the same 

 time he endeavours to show that those parts must always vary 

 which are no longer well adapted to the conditions of life. 



I am afraid, however, that Brooks is confounding two things 

 which are in reality very different, and which ought necessarily 

 to be treated separately if we wish to arrive at correct con- 

 clusions : viz., the adaptation of a part of the body to the body 

 itself, and its adaptation to external conditions. The first of 

 these adaptations ma}^ exist without the second. How can 

 those parts become variable which are badly adapted to the 

 external conditions, but are nevertheless in complete harmony 

 with the other parts of the body? If the conditions of life of 

 the cells which constitute the part in question must become un- 



1 1. c, p. 82. 

 z 



