I9I2] STOCKARD— CONTROL OF DEVELOPMENT. 193 



innate changes in the germ-plasm but even these when fully under- 

 stood may possibly be shown to result indirectly from some change 

 in the chemical surroundings. 



First to consider the modifications induced in the developing egg 

 or embryo by a strange chemical environment. It has been found 

 for the eggs of a number of animals that develop normally in sea- 

 water that when certain chemicals are added to their environment 

 they develop into various unusual forms. 



I experimented for several years on fish's eggs and found that 

 on adding any one of a large series of salts to the sea-water that 

 the eggs developed abnormally and gave rise to a great number of 

 monstrous individuals. The types of the monstrosities were vari- 

 able, and the same kind of monster often resulted from different 

 treatments. This was to be expected, but the important problem 

 was to produce some definite type of monster in great numbers 

 with any given treatment. This I finally succeeded in doing and in 

 some experiments got as many as 90 per cent, typical Cyclopean 

 or monophthalmic monsters. These types of monsters first occurred 

 in solutions of MgCL in sea-water. In such solutions as many as 

 50 in 100 eggs formed one-eyed cyclopean embryos. Since Mg 

 has the power to inhibit activity in animals and so acts as an anaes- 

 thetic I determined to try the action of a number of such substances 

 on the developing eggs to ascertain whether they might also inhibit 

 the lateral migration of eye parts. Alcohol, ether, chloroform, 

 chloreton, etc., were employed and cyclopean monsters resulted from 

 eggs developing in all of these substances. Alcohol gave the most 

 decided effects and inhibited the normal production of eyes in almost 

 all cases. All of these anaesthetics act more particularly upon the 

 central nervous system of the adult and it is important to find that 

 the development of the nervous system is also especially affected 

 by them. In alcohol solutions the embryos showed almost every 

 gross abnormality of the brain which is known to occur, and the 

 spinal cord was often defective. 



I have repeated the experiments of Fere with hen's eggs and find 

 that when these eggs are exposed to fumes of alcohol many abnormal 

 chicks result. When hen's eggs are placed in closed dishes over 



