IN THE THEORY OF NATURAL SELECTION. 



how could such an unfavourable development afford the occasion 

 for the throwing- off of gemmules, and a resulting variability 

 of the spines, inasmuch as the epidermic tissue in which these 

 structures arise, remains under completely normal and favourable 

 conditions, whatever length or sharpness the spines may attain ? 

 The conditions of the epidermis are not unfavourably affected 

 because, as the result of short and blunt spines, the number of 

 hedgehogs is reduced to far below the average. Or consider the 

 case of a brown caterpillar which would gain great advantage by 

 becoming green ; what reason is there for believing that the cells 

 of the skin are placed in unfavourable conditions, because, in 

 consequence of the brown colour, far more caterpillars are detected 

 by their enemies, than would have been the case if the colour 

 were green ? And the case is the same with all adaptations. 

 Harmony between the parts of the organism is an essential con- 

 dition for the existence of the individual. If it is wanting, the 

 individual is doomed ; but such harmony between any one part and 

 all others, i. e. proper nutrition for each part, and adequate per- 

 formance of its proper function, can never be disturbed by the 

 fact that the part in question is insufficiently adapted to the outer 

 conditions of life. According to Darwin, all the cells of the body 

 are continually throwing off gemmules, and against such an 

 assumption no similar objection can be raised. It can only be 

 objected that the assumption has never been proved, and that it 

 is extremely improbable. 



A further essential difference between Darwin's theory of 

 pangenesis and Brooks' hypothesis lies in the fact that Brooks 

 holds that the male and female germ-cells play a different part, 

 and that they tend to become charged with gemmules in different 

 degrees, the egg-cal containing a far smaller number than the 

 sperm-cell. According to Brooks the egg-cell is the conservative 

 principle which brings about the permanent transmission of the 

 true characters of the race or species, while he believes that the 

 sperm-cell is the progressive principle which causes variation. 



The transformation of species is therefore believed to take place, 

 for the most part, as follows: those parts which, are placed in 

 unfavourable conditions by the operation of external influences, 

 and which have varied, throw off gemmules which reach the 

 sperm-cells, and the latter by fertilization further propagate the 



