ENVIRONMENT INFLUENCING DEVELOPMENT 309 



bees, a given egg may develop either into a worker or into a queen. 

 This development depends upon the nourishment that the larva 

 receives. It is thought by some investigators that the kind of food 

 (honey or pollen) may cause the differentiation in the growing larva. 

 Others think that when a larva is given large amounts of foods, it 

 becomes a queen ; if a small amount of food, it becomes a worker. 



Many abnormal forms result from a variety of unfavorable con- 

 ditions during development. This is true in human beings as well 

 as in other species. Even where the results are not abnormal, 

 inequalities of environment bring about differences among individ- 

 uals of the same species. For example, lack of Vitamin D in the 

 diet results in bone deformities. Lack of iodine may give rise 

 to cretins. Too much food is likely to make people fat. 



Trees may become distorted by the wind. Plants grown in 

 poorly-lighted places show an irregular development as the result 

 of a one-sided illumination. Well-fed cows give more milk than 

 poorly-fed cows. The lizards and spiders of Mammoth Cave, 

 Kentucky, are colorless. Exposure to sunlight is thought to 

 increase the amount of pigment in the human skin. One who has 

 learned to swim behaves differently in the water from one who 

 has not learned to swim. A trained horse runs faster than an 

 untrained horse of the same parentage. A child who has re- 

 covered from measles does not get the disease a second time 

 when exposed to the infection. One can become accustomed to 

 cold weather or to rainy climate. One can become skillful in 

 some art or game as a result of practice; or his muscles can 

 become weak after a period of disease or disuse. 



Where the differences between two individuals result from 

 differences in outward conditions, or from environment, the prac- 

 tical problem is to find out how to treat plants or animals so as to 

 get the desired results. Will one kind of fertilizer or mineral salts 

 result in more cotton per acre ? Will one kind of food produce more 

 milk per cow? If so, an adjustment can be made so that the 



