The Life-History and Anatomy of Butterflies 



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himself more thoroughly and accurately as to the internal anat- 

 omy of these insects may consult with profit some of the treatises 

 which are mentioned in the list of works dealing with the sub- 

 ject which is given elsewhere in this book. 



Polymorphism and Dimorphism. Swedes of butterflies often 

 show great differences in the different broods which appear. The 

 brood which emerges in the springtime from the chrysalis, which 

 has passed the winter 



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under the snows, may 

 differ very strikingly 

 from the insect which 

 appears in the second or 

 summer brood; and the 

 insects of the third or 

 fall brood may differ 

 again from either the 

 spring or the summer 

 brood. The careful stu- 

 dent notes these differ- 

 ences. Such species are 

 called polymorphic, that 

 is, appearing under dif- 

 ferent forms. Some spe- 

 cies reveal a singular 

 difference between the 

 sexes, and there may be 

 two forms of the same 

 sex in the same species. 

 This is most common in 

 the case of the female 

 butterfly, and where 

 there are two forms of 

 the female or the male 

 such a species is said to 

 have dimorphic females 

 or males. This phenomenon is revealed in the case of the 

 well-known Turnus Butterfly; in the colder regions of the 

 continent the females are yellow banded with black, like the 

 males, but in more southern portions of the continent black 

 females are quite common, and these dark females were once 



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