THE WONDER OF LIFE 599 



caused by living in a particular kind of solution. The 

 reduction was found to persist for a short time, and was 

 followed by a reaction. 



The experiments illustrate ' parallel induction.' In the 

 first and second sets of experiments, at any rate, individuals 

 placed in abnormal environments in their first stage 

 acquired the definite abnormal features in their own bodies 

 in later stages. Simultaneously, the eggs in their ovaries 

 were influenced in such a way that the young developed 

 from them presented at birth the same abnormaUty as 

 that which their parents had acquired in their Ufetime. 

 It made Httle difference whether the young developed 

 from eggs laid after removal of the parents to control 

 conditions, or were bom in the abnormal environment, 

 so long as the eggs underwent their ovarian growth while 

 the parents were under the influence of the environment. 

 In the subsequent broods of those parents which had been 

 removed to control conditions the effect of the abnormal 

 conditions appeared in rapidly diminishing intensity. In 

 the second generation in control conditions the abnormal 

 effect still persisted (in the first two sets of experiments), 

 but to a very slight degree. In all three sets of experiments 

 a very decided reaction appeared in the third generation. 



Mutations, giving rise to new types, are due to a change 

 in the composition in the Mviag unit. ' The other cause 

 of variation — a change in the environment while the living 

 units remain the same — ^is probably far commoner. Such 

 a change, if effective, will probably result in the formation 

 of unusual metaboUc products included in the living proto- 

 plasm, and thus the visible external variation produced 

 may have as its immediate cause either the changed environ- 

 ment itself, or the altered protoplasmic inclusions. In 



