34 ZOOLOGV 



enemies — the Ynixh — by a disagreeable taste, and their 

 briglit colors serve to remind birds of their inedilile nature 

 and so afford them greater immunity from attack. But this 

 can hardly be a complete explanation of the color of 

 Lepidoptera, for many nocturnal species have strikingly 

 beautiful color patterns. We shall consider directlj^ some 

 special uses to which the coloration of Lepidoptera has been 

 put. 



The Broods of Butterflies and their Polymorphism. — 

 Butterflies wnter over in various stages, .some in the egg stage, 

 some as larvie, others as pupa; or as imagos. Some kinds 

 pass the mnter in either of two stages. In whatever stage 

 they tarry, the life current runs very slow, and during this 

 season few changes take place. In the spring, development 

 goes on rapidly : the winter generation becomes mature and 

 a summer generation is started. Frequently there is more than 

 one lirood produced during the summer, even in the Northern 

 States. Farther south two and even three summer broods are 

 still commoner. Where two or three broods occur they may be 

 quite dissimilar. This is very strikingly illustrated in the case 

 of the Zelira Swallow-tail (Papilio ajax) of the southeastern 

 United States, which has more than one brood each year. 

 The early spring form (" marcellus " form) is the smallest, 

 and has the tail tipped with white ; the summer form (" ajax ") 

 is the largest, and has the tail two-thirds longer than the 

 marcellus form. (Ither illustrations of this seasonal difference 

 are given by the imported Cabbage Butterfly, the Gray-veined 

 White, and the Spring Azure. This dissimilarity between the 

 broods of different seasons is known as " seasonal dimorphism " 

 or " polymorphism." The cause of the difference between 

 the different broods seems to be the dissimilar weather 



