II.] INCIPIENT STRUCTURES. 39 



In these cases of mimicry it seems difficult indeed to 

 imagine a reason why variations tending in a minute degree 

 in any special direction should be preserved. All varia- 

 tions would be preserved wliich tended to obscure the 

 perception of an animal by its enemies, whatever direction 

 those variations might take, and the common preservation 

 of conflicting tendencies would greatly favour their mutual 

 neutralization and obliteration if we may rely on the many 

 cases recently brought forward by Mr. Darwin with regard 

 to domestic animals. 



Mr. Darwin explains the imitation of some species by 

 otliers more or less nearly allied to them, by the common 

 origin of both the mimic and the mimicked species, and the 

 consequent possession by both (according to the theory of 

 " Pangenesis ") of gemmnles tending to reproduce ancestral 

 characters, which characters the mimic must be assumed 

 first to have lost and then to have recovered. Mr. Darwin 

 says,^ " Varieties of one species frequently mock distinct 

 species, a fact in perfect harmony with the foregoing cases, 

 and explicable onlj/ on the theory of descent." But this at 

 the best is but a partial and very incomplete explanation. 

 It is one, moreover, which Mr. Wallace does not accept.^ 

 It is very incomplete, because it has no bearing on some 

 of the most striking cases, and of course Mr. Darwin does 

 not pretend that it has. We should have to go back far 

 indeed to reach the common ancestor of the mimicking 

 walking-leaf insect and of the real leaf it mimics, or the 

 original progenitor of both the bamboo insect and the 

 bamboo itself. 



As these last most remarkable cases have certainly 



1 "Animals and Plants under Domestication," vol. ii. p. 351. 



2 Loc. cit. pp. 109, 110. 



