462 Proceedings of the Royal Physical Society. 



to be plausibly referable to direct environmental influence. 

 In other cases the organism asserts itself, in relation to the 

 environment, by what may be described as a thrust. Now, 

 without denying the possibility of distinguishing distinctly 

 internal or independent organismal variation, it is necessary 

 to admit the possibility of environmental influences remain- 

 ing long dormant, being slowly added up within the organism 

 until they finally express themselves in what, in one sense, 

 comes from within, but, in another sense, comes as truly from 

 without. 



(4.) When animals are kept in a confined space, or in other 

 changed external conditions, it has been shown that a pigmy 

 brood may be the result. But this only shows itself in the 

 course of generations. The transition from one species of 

 brine-shrimp to another, effected by altering the salinity of 

 the water, required a succession of generations. It seems 

 probable that this must have been the case in all the supposed 

 environmental modifications, which have been of historic 

 importance. Thus we may define a fourth category of en- 

 vironmental variations, which may not be very appreciable in 

 the individual, except in affecting the rej)roductive elements, 

 through which the changes become expressed in the offspring. 

 Barfurth (224), for instance, notes how in the trout the 

 absence of suitable spawning ground conditions (1st) reten- 

 tion of ova ; (2d) degeneration and absorption of reproductive 

 material ; (3d) hypertrophy of ovary ; and (4th) the size and 

 health of future offspring. 



(5.) Lamarck and others have ascribed to the environment 

 an important indirect action, inasmuch as changed conditions, 

 without directly hammering any change upon the organism, 

 provoke increase, decrease, or alteration of function, in 

 response to which changes of structure ensue. An alteration 

 in the food-supply may bring about a direct change in the 

 line of starvation or hypertrophy; but it may also simply 

 induce the animal to exert itself, more or less, in order to 

 acquire the requisite nutrition. 



(6.) Wagner and others have allowed the importance of 

 the environment in producing passive distribution, i.e., dis- 

 tribution in which the organisms were not themselves active. 



