THE BUTTERFLIES AND MOTHS 



59 



dimorphism (Gr. di-, "two" ; morphe, "form") if the varia- 

 tions show two well-marked types ; and as polymorphism (Gr. 

 poly, "many") if there are several different variations. In 

 many species the males differ greatly from the females; 

 this is called sexual dimor- 

 phism. Many examples are 

 known in which broods of 

 the same butterfly appear 

 at two different seasons. 

 These broods often differ 

 widely in size and color 

 markings. This is known 

 as seasonal dimorphism. In 

 some cases seasonal dimor- 

 phism and polymorphism 

 are associated with changes 

 of temperature. The zebra 

 swallowtail {Iphicli'des 

 marcel'lus), which is ex- 

 tensively distributed in the 

 eastern United States, 

 has three different forms : 

 the early-spring form, the 

 late-spring form, and the 

 summer form. The spring 

 forms appear from pupae 

 which have lived through the winter. From the eggs 

 which the spring forms lay the summer form is developed. 

 Cabbage Butterflies. Very familiar to all is the white or 

 slightly yellowish butterfly seen so commonly flitting over 

 the gardens from early spring until late in the fall. This 

 is the common cabbage butterfly (Pi'eris ra'pse), so called 



1 Reprinted by permission from Applied Entomology, by H. T. Fernald, pub- 

 lished by the McGraw-Hill Book Company, Inc. 



Mil' 



% 





Fig. 40. Cabbage butterfly 



a, adult ; b, eggs, side and end views (much 

 enlarged) ; c, larva ; d, chrysalis l 



