^^^ ZOOGENESIS "^^^^ 



dark in color with short wings. They are more or 

 less sedentary and seldom stray far from their place of 

 origin. The autumn individuals, however, which 

 live through the winter, are much lighter in color 

 than the summer individuals and have longer wings. 

 These wander very widely. The dark short-winged 

 and light long-winged forms are very different from 

 each other and never intergrade. 



A somewhat similar phenomenon is seen in the pro- 

 duction of a long-winged migratory form from time 

 to time, or more or less irregularly, by certain grass- 

 hoppers. Similar and comparable phenomena are also 

 seen in other insects. 



In various regions certain butterflies have very 

 distinct alternative forms one flying in the wet and 

 the other in the dry season. These forms are usually 

 quite distinct, but in many cases intergrades occur, 

 and in a few intergrades are common. 



Some of our butterflies in certain years will produce 

 typical wet forms in bogs or other damp localities 

 which die out without leaving any progeny. Such 

 forms with us are usually regarded as extreme varieties 

 or aberrations according to their relative abundance. 



In most of our butterflies the individuals of the 

 spring brood increase gradually in size and change 

 more or less noticeably in color — showing especially 

 an increase in the dark markings — from the earliest 

 to the latest. This change is very marked in the 

 common cabbage and yellow clover butterflies, and 

 also in the zebra and the yellow swallowtails. The 

 color changes are perhaps most striking in the com- 



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