172 Heredity and Environment 



the same environment one egg becomes a chicken and another a 

 duck; one becomes a frog and another a fish and another a 

 snail; one becomes a black guinea-pig and another a white one; 

 one becomes a male and another a female ; one gives rise to a tall 

 man and another to a short man, etc. Since these differences may 

 occur in the same environment they must be due to differences in 

 the germ cells concerned. 



Environment Non-specific. On the other hand different en- 

 vironmental conditions may be associated with similar develop- 

 mental results. Loeb and others have found that artificial par- 

 thenogenesis may be induced by a great variety of environmental 

 stimuli, viz., by salt solutions, by acids and alkalis, by fatty acids 

 and fat solvents, by alkaloids and cyanides, by blood serum and 

 sperm extract, by heat and cold, by agitation and electric current. 

 There is certainly nothing specific in these different stimuli. 

 Similarly Stockard has discovered that cyclopia, or one-eyed 

 monsters, may be produced by magnesium salts, alcohol, chlore- 

 tone, chloroform, and ether, and to this list McClendon has 

 added various other salts and anaesthetics. In all such cases it is 

 evident that the specific results of such treatment are due to a 

 specific organization of the germ rather than to specific stimuli, 



Why does one egg give rise to a chicken and another to a duck, 

 or a fish, or a frog? Why does one egg give rise to a black guinea- 

 pig and another to a white one, though both may be produced by 

 the same parents ? Why does one child differ from another in the 

 same family ? Why does one cell give -rise to a gland and another 

 to a nerve, one to an egg and another to a sperm? If these dif- 

 ferences are not due to environmental causes, and the evidence 

 shows that they are not, they must be due to differences in the 

 structures and functions of the cells concerned. 



Protoplasm Specific. Many differences in the material sub- 

 stances of cells are visible, and many more are invisible though 

 still demonstrable. These differences may not be detectable by 

 chemical or physical tests, and yet they may be demonstrated 



