444 SOME GENERAL PROBLEMS OF DEVELOPMENT 



Lamarckian Theory of the inheritance of acquired characteristics 

 maintains that differences acquired by the individual as a result 

 of changes in the environment may become a part of its inheritance 

 and thus be transmitted to future generations. The majority of 

 biologists, however, do not believe that the evidence justifies such 

 a conclusion. 



In the higher organisms, where the effects of habit formation are 

 much in evidence, the influences referred to in the preceding para- 



FiG. 23L — Effect of environmental conditions upon development of a fish 



Fiindulut;. 



Above, a normal free-swimming embryo from dorsal view. Below, cyclopean monster, with 

 the two eyes grown together ventrally and anterior to the mouth (w), as developed in sea 

 water to which magnesium salts had been added. (After Stockard, Anatomical Record, 

 Vol. III.) 



graph as factors of environment are further complicated by the 

 effects of training, as when a horse is trained to trot, a dog to fetch 

 and carry, or a child to read and write. The relationships of the 

 factors involved, including that of heredity, are often represented 

 by a triangle (Fig. 232) in which the base represents the factor of 

 heredity, or what the organism is potentially, and the sides the 

 environmental factors, which may be conveniently divided into the 

 influence of the surroundings, or what the organism has during its 

 lifetime, and its training, or what it does. The shape and size of 

 such a triangle, therefore, shows what the individual becomes in its 

 final adult stages. Modifications of the sides and base show what 

 can be done by various combinations of the fundamental heredi- 

 tary factor and the two environmental factors in the production 

 of an individual. 



