36 GENETICS AND EUGENICS 



as contrasted with normal temperatures. While the bodies 

 of the parents remained unaffected, the coloration of their 

 offspring varied with conditions of temperature and moisture 

 during the growth and fertilization of the eggs which pro- 

 duced those offspring. Tower therefore concludes that the 

 germ-plasm was directly and permanently affected by varia- 

 tions in the environment during a particular sensitive growth 

 period of the egg. This work is therefore no argument for the 

 inheritance of acquired characters; nevertheless it is an argu- 

 ment for evolution directly guided by the environment, which 

 after all is the essence of Lamarckism. There are several 

 reasons why we should accept Tower's conclusions with some 

 reservation. 



1. In the first place his experiments are not reported in 

 sufficient detail to enable us to form a critical opinion as to 

 their conclusiveness. 



2. If the supposed temperature and moisture effects are 

 due solely to those conditions, they should appear equally in 

 all eggs subjected to the same conditions, but this is not the 

 case. Only certain individuals are modified. Since this is so, 

 it is evident that all the eggs were not alike at the outset, for 

 some were more sensitive than others to temperature and 

 moisture changes in the environment, if indeed these were 

 the agencies which caused the changes observed. A good 

 argument could therefore be made for considering the tem- 

 perature and moisture changes as merely selective agencies 

 exerted on a collection of germ-cells already inherently vari- 

 able in their potentialities. For Tower maintains that the 

 variations once obtained are perfectly stable for an indefinite 

 number of generations. His claim, therefore, is that by direct 

 action of the environment for a comparatively brief period j 

 permanent changes in the germ-plasm may be brought about. 



It would seem that if the germ-plasm is thus directly modi- 

 fiable, the action ought to be reversible. Changes of environ- I 

 ment should unmake species as readily as they make them, 

 yet such a result would scarcely harmonize with Tower's 



