CLASSIFICATION 231 



the value of the groups in several classes (and all our 

 experience shows that their valuation is as yet arbitrary), 

 could easily extend the ])arallelisin over a wide range; 

 and thus the septenary, quinary, quaternary and ternary 

 classifications have probably arisen. 



There is another and curious class of cases in which 

 close external resemblance does not depend on adaptation 

 to similar habits of life, but has been gained for the sake 

 of protection. I allude to the wonderful manner in 

 which certain butterflies imitate- as first described by 

 Ml'. B.itej, other and quite distinct species. This excel- 

 lent observer has shown that in some districts of South 

 America, where, for instance, an Ithomia abounds in 

 gaudy swarms, another butterfly, namely, a Leptalis, 

 is often found mingled in the same flock; and the latter 

 so closely resembles the Ithomia in every shade and 

 stripe of color, and even in the shape of its wings, that 

 Mr. Bates, with his eyes sharpened by collecting during 

 eleven years, was, though always on his guard, continu- 

 ally deceived. When the mockers and the mocked are 

 caught and compared, they are found to be very diflEerent 

 in essential structure, and to belong not only to distinct 

 genera, but often to distinct families. Had this mimicry 

 occurred in only one or two instances, it might have 

 been passed over as a strange coincidence. But, if we 

 proceed from a district where one Leptalis imitates an 

 Ithomia, another mocking and mocked species belonging 

 to the same two genera, equally close in their resem- 

 blance, may be found. Altogether no less than ten 

 genera are enumerated which include species that imitate 

 other butterflies. The mockers and mocked always in- 

 habit the same region*, we never find an imitator living 



— Science — 27 



