THE CELLULAR BASIS 153 



sperm extract, by heat and cold, by agitation 

 and electric current. There is certainly noth- 

 ing specific in these different stimuli. Simi- 

 larly Stockard has discovered that cyclopia, 

 or one-eyed monsters, may be produced by 

 magnesium salts, alcohol, chloretone, chloro- 

 form, and ether. 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 an- 

 other to a sperm? If these differences 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. 



Many differences in the material substances 

 of cells are visible, and many more are invisi- 



