SIDELIGHTS ON THE LEPIDOPTEROLOGICAL WORK OF THE CENTURY. 33 



error from " convergence," i.<\, the close resemblance in one or more 

 characters of widely separated species, which adds much to the diffi- 

 culties experienced. It is common in comparing schemes of descent 

 based on different characters, to be tempted to suppose that the two 

 lines mingled again by some sort of crossing. This is, of course, absurd, 

 but it shows that the real line of descent is more lengthy and compli- 

 cated than either of our separate tables contemplated. Such approach 

 as we may ultimately make to a knowledge of the true phyletic lines, 

 will of course be founded on researches into many more characters that 

 are yet available, and will be correspondingly more lengthy and 

 complicated. 



I do not wish to overlook the fact that a knowledge of evolution 

 was more than foreshadoAved at the beginning of the century, or even 

 twenty centuries since, but the change in our attitude towards it could 

 hardly be greater than it is, were it then unheard of. We are not 

 satisfied to know simply that species A has a white mark, while species 

 B has a black one. We must find out in what the difference consists 

 structurally, by what organic changes the present structure might have 

 been reached from one previously common to both, what forces may have 

 acted on each to produce such changes, what the uses are of the diffe- 

 rences, how long they took for their production, how stable they may 

 be, how far they are variable ; these and many other similar questions 

 can rarely be fully answered, but they suggest many observations and 

 experiments to be made on the structure, habits, itc, of both species, 

 and of many others related or not related to them. 



It would not perhaps be a very laborious matter to index and 

 classify all the entomological work of this character that was available 

 at the beginning of the century. We may perhaps take Kirby and 

 Spence's Introduction, as containing, with other matters, a very full 

 summary of everything that Avas then known, perhaps a thousand 

 volumes would not set forth our present knowledge in equal amplitude. 

 This greater extent of our present knowledge, which compels each of 

 us to take but a fractional part of the whole field in which to disport 

 himself, is not however entirely, not perhaps even very greatly, to 

 be attributed to the stimulus of having a satisfactory theory to guide 

 our work. The records of research of all sorts accumulate not in 

 arithmetical but in geometrical progression. On the physiological and 

 anatomical side this may be attributed to the great advance in micro- 

 scopical technique as the most important element, but in that and other 

 fields, it depends on the same causes as all other progress during 

 the century. Increase of population, in wealth, and in education, 

 facilities of travel, and of intercommunication, have led to more persons 

 working on material from all over the world, easily publishing and 

 comparing results, affording new starting-points to fresh workers and 

 so on. Up till the last twenty years Germany probably led us in most 

 researches on habits, structure, distrilnition and everything else related 

 to entomology generally, and to the modern aspects of the subject, but 

 now there is little question that America is going to the front. Much 

 of the American work no doubt has an economic character as its base, 

 and has corresponding limitations. Much of it is also no doubt 

 systematic in the limited sense of merely adding to the lists of known 

 species, inevitable in the exploration of so great an area of new ground. 

 Still, it is quite clear that America challenges for the first place, when 



