LEPIDOPTERA OF NEW YORK AND NEIGHBORING STATES 9 



which an earlier category is divided. In the case of a tribe or larger 

 group, whose name is derived from that of a genus, the subdivision in 

 which that genus remains holds its name. When, however, a genus is 

 divided, a species typical of the genus is taken (the type), which shall 

 always be included in the genus retaining the old name. In many cases 

 the proposer of a genus has designated the type ; in others, the selection 

 has been left to a later worker, and there is a good deal of confusion 

 as to its selection. Thi,s confusion has been the basis of most of the 

 changes of name of familiar insects with which the worker on Lepi- 

 doptera is cursed. 



In the present memoir we are dealing with part of a single order, 

 the Lepidoptera, belonging to the class Insecta. The suborders, super- 

 families, families, subfamilies, tribes, genera, subgenera, and species 

 are all systematically arranged in the text, and need no further 

 explanation. 



VARIATION 



A species is, next to an individual, the most fundamental unit of 

 living nature ; but species themselves are not homogeneous. For inter- 

 crossing, which tends to bring things to an average, is offset by varia- 

 tion, which is continually producing new forms. 



Although not as a rule striking, and often ill-defined, the most funda- 

 mental subdivision of a species is the race (also called subspecies, or 

 variety, as that word is used by many German and English workers) ; 

 these are forms isolated by difference of locality or habitat. Races are 

 more or less clearly defined according to the amount of intercrossing 

 between them; and this, in its turn, is a function of both the distances 

 involved and the mobility of individuals. Some stocks, also, appear 

 to be inherently more variable than others. So an active species, like 

 Vanessa cardui, has few races, though its distribution is almost world- 

 wide; while in the case of some Lycsenas and Haploas, each patch of 

 ground has its local form a little race distinct from those around 

 it. Such minute races are known as strains. In general, races are 

 distinguished from each other by a large number of minute characters, 

 none of which are wholly constant, so that occasionally there will be 

 found, in any region, forms that belong rather to some other race. 

 Races breed true, at least so long as their environment remains constant. 



Another type of variation is seasonal. Many species have more than 

 one generation a year ; and in that case specimens from one season are 

 often recognizably, and sometimes strikingly, different from those 

 of another. This variation is usually a response to the weather, 

 wholly or in part, so that it is not very rare for a form normal, perhaps, 

 in the spring, to appear in a cold summer, or in a cold breeding cage, 

 or even erratically if the individual larva has grown up and trans- 



