IN BUTTERFLIES 251 



sensible humidity. The oscillations of the condi- 

 tions are greater, and they vibrate through long 

 measures above and below the average. All the 

 irregular as well as regular changes are of this 

 sort, and the European observer defines the climate 

 as directly antagonistic to that he has left." These 

 differences, however, as Humboldt and others long 

 ago pointed out, have a broader bearing than the 

 above statements would imply ; for they are char- 

 acteristic of the eastern shores of both worlds as 

 opposed to the western, the meteorological phe- 

 nomena of the eastern United States being almost 

 precisely paralleled by those of northern China, 

 where great excesses of temperature occur, with 

 wide variability, long summers and winters, and 

 rapid transitions. 



Perhaps on these grounds we can most simply 

 account for the difference in the number of broods 

 in certain butterflies on the two continents ; but, 

 if so, then it follows that we ought to anticipate 

 similar differences between the broods of some of 

 the species found both in Europe and in eastern 

 Asia ; a point about which we can assert absolutely 

 nothing, for want of data. These grounds, how- 

 ever, will certainly be insufficient to account for 

 the differences to which we have alluded in man ; 



