THE GERM-PLASM THEORY 81 



image which, indeed, apparently may satisfy the 

 craving for causality (to satisfy which it was in- 

 vented), but which eludes the control of concrete 

 thought, by dealing with a complexity that is 

 latent and perhaps only imaginary. Thus, craftily, 

 they prepare for our craving after causality a 

 slumbrous pillow, in the manner of the philo- 

 sophers who would refer the creation of the world 

 to a supernatural principle. But their pillow of 

 sleep is dangerous for biological research ; he who 

 builds such castles in the air easily mistakes his 

 imaginary bricks, invented to explain the com- 

 plexity, for real stones. He entangles himself in 

 the cobwebs of his own thoughts, which seem to 

 him so logical, that finally he trusts the labour of 

 his mind more than nature herself." * 



Poor Weismann ! this was " the most unkindest 

 cut of all," that he should be reckoned as no better 

 than one of those who believe in a Divine Creator. 



But we have not yet done with our " vital units " 

 and their performances. They not merely exist, 

 side by side, in that microcosm the germ-cell, 

 says their inventor, but they war ceaselessly with 

 one another. This struggle between the vital units 

 is the process of " germinal selection " which 

 Weismann postulates in order to account for the 

 occurrence of variations and to explain how the 

 environment can act on the germ. There are, he 

 says, marked fluctuations in the nutritive stream 

 supplied to the germ-plasm as it lies in the body ; 

 fluctuations which may be, and, in many cases, 



* The Biological Problem of To-day, p. 1 1 . 



