2i6 CONTINUITY. 



genera of this group have been founded, and even in some 

 instances those of its orders. 



II. The ordinary notion of species as assemblages of indi- 

 viduals marked out from each other by definite characters that 

 have been genetically transmitted from original proto-types 

 similarly distinguished, is quite inapplicable to this group ; 

 since even if the limits of such assemblages were extended so 

 as to include what elsewhere would be accounted genera, they 

 would still be found so intimately connected by gradational 

 links that definite lines could not be drawn between them. 



III. The only natural classification of the vast aggregate 

 of diversified forms which this group contains will be one 

 which ranges them according to their direction and degree of 

 divergence from a small number of principal family types ; 

 and any subordinate grouping of genera and species which 

 may be adopted for the convenience of description and nomen- 

 clature must be regarded merely as assemblages of forms 

 characterised by the nature and degree of the modifications 

 of the original type, which they may have respectively 

 acquired in the course of genetic descent from a common 

 ancestry. 



IV. Even in regard to these family types it may fairly be 

 questioned whether analogical evidence does not rather favour 

 the idea of their derivation from a common original than that 

 of their primitive distinctness. 



Mr. H. Bates, when investigating ' The Lepidoptera of the 

 Amazon Valley/ may almost be said to have witnessed the 

 origin of some species of butterflies, so- close have been his 

 observations on the habits of these animals that have led to 

 their variation and segregation, so closely do the results follow 

 his observations, and so great is the difficulty of otherwise 

 accounting for any of the observed facts. 



In the numerous localities of the Amazon region certain 

 gregarious species of butterfly (Heliconided) swarm in incre- 

 dible numbers, almost outnumbering all the other butterflies 

 in the neighbourhood ; the species in the different localities 

 being different, though often to be distinguished by a very 

 slight shade. 



