Influence of Environment 169 



darker forms which are rather distinct in Brazil and Vene- 

 zuela and in Honduras, and have been given specific names 

 accordingly. By means of experiments, it was possible to 

 show that the pigmentation of these birds is directly in- 

 fluenced by the moisture of the atmosphere. By controlling 

 the moisture, it is possible to develop any one of these types. 

 Among the divergent types of fruit flies in Morgan's 

 cultures was one in which the abdomen was misshapen. 

 When a culture of these flies is allowed to develop in a rela- 



FiG. 42. Abnormal Abdomen in Fruit Fly 



A race of flies has appeared in the experimental study of heredity, with a dis- 

 tinctly mis-shapen abdomen. Normal and abnormal male, a and b; normal and 

 abnormal female, c and d. This strain can be raised so that the abdomen will 

 appear normal or abnormal, as conditions of nutrition are m.odified, whereas the 

 wild strain will develop individuals with normal abdomen under all conditions. 

 After Morgan, The Physical Basis of Heredity, published by J. B. Lippincott 

 Company. 



tively dry atmosphere the abdomen appears in every way 

 normal. A batch of eggs from a given mother may be di- 

 vided, one part being placed in a moist atmosphere and the 

 other in a relatively dry atmosphere, with the result that 

 the former batch will show the abnormal abdomen while the 

 latter will appear normal (Fig. 42). 



These various modifications show the more or less di- 

 rect influences of the environment, although they are also 

 in many details adaptive responses to the environment. A 

 lowered temperature results in stunting the growth of a 

 plant. This we can find through experiment to be a purely 

 physico-chemical result. A lowered temperature will in 



