INTRODUCTION 35 



catch it. The most notable example of such mimicry in 

 North America is that of the Monarch butterfly, which is 

 supposed to be the distasteful species, and the Viceroy 

 butterfly, which is supposed to mimic it. Several other 

 instances of mimicry are found among our own butterflies, 

 while in South America, Africa, and Asia there are number- 

 less examples. 



Heliotropism 



It has long been known that the green surfaces of plants 

 respond to the stimulus of the sun's rays in a most remark- 

 able manner. This response has commonly been called 

 heliotropism and it has been carefully studied by botanists 

 all over the habitable world. More recently, the fact has 

 been observed that many animals respond in certain defi- 

 nite ways to the stimulus of direct sunshine and the same 

 term has been applied in this case. Very little attention 

 has been given to the subject of heliotropism until within a 

 few recent years. But the observations which have been 

 made by Parker, Longstaff, Dixey, and others open up a 

 most interesting field for further observation. An ad- 

 mirable summary of our present knowledge of the subject 

 has been published by Dr. Longstaff in his book "Butterfly 

 Hunting in Many Lands." 



One of the earliest observations upon this subject was 

 that published in my book "Nature Biographies" which ap- 

 peared in June, 1901, concerning the habit in the Mourning 

 Cloak: "On a spring-like day early in November (the 8th) 

 I came across one of these butterflies basking in the sun- 

 shine upon the ties of a railway track. It rested with its 

 wings wide open. On being disturbed, it would fly a short 



