DIMINISHING ENVIRONMENTAL INFLUENCE 323 



this is true we should not expect any changes in the other organs of the 

 body, since these other organs have not experienced any change from 

 their normal environment. If, on the other hand, the environment is 

 actually and certainly changed, as is the case when caterpillars are fed 

 on different kinds of food, the variations associated with sex may, to a 

 certain extent, be artificially induced. 22 It is very doubtful if the verte- 

 brates will permit any such modification of sexual differences by changes 

 in their diet. 



Fishes 



One of the first points noticed in looking over the results of modifi- 

 cation experiments on fishes is that the total number of such experi- 

 ments is significantly small. There is little to record that can in any 

 way be considered striking or interesting as bearing on the present dis- 

 cussion. 



If the under surface of flounders is exposed to light during the 

 growth of the fish the side which is normally white will become pig- 

 mented like the upper side, though not so much so. 23 Here we see that 

 what is perhaps the most striking modification produced in a fish is 

 concerned merely in a change of pigmentation, which is probably always 

 one of the easiest changes to bring about. 



In hatcheries, it is sometimes desirable to retard the growth of 

 fishes for commercial reasons. The experiments of Meyer, Earll, Eice 

 and others show that lowering the temperature of the water lengthens 

 the interval between fertilization and hatching to about a month. 

 There are no further facts to show whether the fishes are permanently 

 modified thereby. Presumably they are normal in the end, as is the 

 case with retarded insects and frogs. Fishes show good regenerative 

 powers and in accordance with their phylogenetic rank. 



Fishes and frogs will not endure the high atmospheric pressure 

 experiments that can be brought to bear upon low invertebrates without 

 loss of life. Although the lower forms which submit to these high 

 pressures (200 to 600 atmospheres) are only temporarily modified and 

 afterwards regain their normal proportions, 24 the facts are significant 

 as showing that higher protoplasm will not submit to the rude and 

 abnormal treatment that the lower will. The higher protoplasm must 

 have its accustomed environment and will not survive if it is ruthlessly 

 forced into very unnatural surroundings. 



Amphibians 

 Within this group one finds modifications brought about by differ- 

 ences in temperature, light, gravity, salt, electricity, atmospheric pres- 



22 Morgan, "Exp. Zool.," p. 437. 



23 Vernon, " Variation," p. 25. 



24 De Varigny, pp. 192-193. 



