170 Changing Plant and Animal Nature 



many mammals and birds bring about a modification of the 

 pigmentation. Among the Chinese primroses are two va- 

 rieties which at ordinary temperatures produce respectively 

 red flowers and white flowers. When the red flower variety 

 is grown at a higher temperature it produces white flowers. 

 The other strain produces only white flowers at any tem- 

 perature in which it will grow at all. Among the hundreds 

 of freak fruit flies which Morgan has found in the course 

 of his studies in heredity is one variety which appears normal 



Fig. 43. Effect of Temperature on Development 



In the butterfly Vanessa levana prorsa the two broods have distinct 

 patterns. By keeping the eggs, larvae, and pupae of the spring brood at 

 a low temperature, it has been possible to make the imagos appear in 

 the fall with exactly the same coloring as the spring brood. This 

 showed that the spring form differs from the summer form because of 

 the influence of the temperature. From Gruenberg, Elementary Biology, 

 published by Ginn & Company. 



if grown at high temperatures but produces supernumerary 

 legs if raised in low temperatures. The exact mechanism 

 at work here is not known, but is also probably a direct action 

 of the temperature upon the physical and chemical processes 

 involved. 



In many flatfish which are typically pigmented on the 

 upper surface and white on the under surface, it has been 

 shown experimentally that the pigmentation is a direct re- 

 sponse to illumination. It is possible to raise flatfish with 

 the upper surface white and the under surface speckled by 

 arranging mirrors in an aquarium so that the fish are illumi- 

 nated from below. In the case of many butterflies the tem- 

 perature to which the larvae or caterpillars are exposed will 

 determine the pigmentation of the adult (Fig. 43) . In some 

 of these modifications brought about by factors in the en- 

 vironment there would seem to be an adaptive value for the 



