384 THE ORIGIN OF SPECIES 



tion is as yet arbitrary), could easily extend the parallelism 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 ex- 

 ternal 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 Mr. Bates, other and quite distinct species. This 

 excellent 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, continually 

 deceived. When the mockers and the mocked are caught and com- 

 pared, they are found to be very different 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 resemblance, may be found. Alto- 

 gether no less than ten genera are enumerated, which include 

 species that imitate other butterflies. The mockers and mocked 

 always inhabit the same region; we never find an imitator Hving 

 remote from the form which it imitates. The mockers are almost 

 invariably rare insects; the mocked in almost every case abounds 

 in swarms. In the same district in which a species of Leptalis 

 closely imitates an Ithomia, there are sometimes other Lepidoptera 

 mimicking the same Ithomia: so that in the same place, species of 

 three genera of butterflies and even a moth are found all closely 

 resembling a butterfly belonging to a fourth genus. It deserves 

 especial notice, that many of the mimicking forms of the Leptalis, 

 as well as of the mimicked forms, can be shown by a graduated 

 series to be merely varieties of the same species; while others are 

 undoubtedly distinct species. But why, it may be asked, are cer- 

 tain forms treated as the mimicked and others as the mimickers? 

 Mr. Bates satisfactorily answers this question by showing that the 

 form which is imitated keeps the usual dress of the group to which 

 it belongs, while the counterfeiters have changed their dress and 

 do not resemble their nearest allies. 



We are next led to inquire what reason can be assigned for cer- 



