SEASONAL POLYMORPHISM. 199 



very hot and dry ones). All this is due to the fact that in each group, 

 be it hi'oad, like Divisions, or more restricted, like Genera, one finds, 

 on the one hand, a tendency to produce a small niDiibcr of genera or of 

 species, as the case may be, irltic/i ih'relop << Iii(ih dcf/ree of adaptability 

 to all sorts of sinroiindiuijs (amongst the Rhopalocera Pi/rameis carditi, 

 L., surpasses all others by its world-wide distribution and its very 

 limited variability), and, on the other hand, a cumparatirely lar(je num- 

 ber, uiore or less /ti<i/tli/ specialised, so that each is adapted to particular 

 conditions. The first are produced by a tendency in evolution to perfect 

 *' functional " elasticity, the latter, on the contrary, it is to be supposed, 

 by " structural " difl:'erences. In 'other words, the first seem to be a 

 development along the line of the catabolic male sex, which reacts to 

 surroundings with a great display of vital force to resist unfavourable 

 conditions, the second seem to be a development along the line of the 

 anabolic female organism, which saves up vital energy, when in per- 

 manent conditions, by creating an organic balance so suited to the 

 latter as to require the least possible exertion in all the functions of 

 life. Of course, the more unsuitable to Lepidoptera the conditions of 

 a locality are, the greater selection will have to take place. That is 

 why the Asiatic species, which have spread as far as the comparatively 

 poor European region, are, as a rule, a selection of representatives of 

 very distinct groups. 



Another necessity which has been felt in the recent revisions of 

 classification is that of an evaluation of the different degrees of 

 relationship between species. It has been realised that all the groups, 

 which were called " genera," were far from being equivalent. This 

 evaluation, of course, can only be made roughly, and one cannot grasp 

 all its shadmgs, but one clearly detects the existence of two grades 

 between the Family and the Genus of old authors ; they have been 

 called Subfamily and Tribe. The tribes often consist in old genera, 

 which have been found to be too distinct and broad, as compared to 

 most other genera, and which have in some cases been divided into 

 smaller ones equivalent to the latter. A more homogeneous distribu- 

 tion of species has thus been attained. In a few cases, notably in the 

 Lycaenidi and T/ieclidi, which include an unusually large number 

 of genera, the latter are found to fall naturally into groups, which can- 

 not be disregarded, although they are not distinct enough to be con- 

 sidered tribes, as Tutt thought them. In our List I will call them 

 " Groups." In the same way a grade of relationship less than the 

 genus is detectable between " groups of species " ; the Parnassius 

 afford an example in the Palaearctic region ; these grades will, how- 

 ever, need a revision of their comparative values to attain uniformity 

 in all the tribes. Let me mention that in the classification of the 

 Lycaenidi tribe I have taken as a base the late Dr. Chapman's conclu- 

 sions, drawn from the study of the genitalia. Two years ago he very 

 kindly corresponded with me about this subject, and it was he who 

 informed me that Tutt had created his genera simply by rule of thumb. 

 Going into the subject more carefully, Chapman had found that the 

 grouping of species and the order suggested by Tutt required rectifica- 

 tion in several cases, which he pointed out to me. Readers must thus 

 not be surprised at some innovations, as were, for instance, the Editors 

 of this Journal, when they observed in a footnote to one of my papers 

 (1920, p. 144), that Jiylas, Esp., and escheri, Hiib., were usually known as 

 Polyommatus, whereas I called them Ayriades. 



