(437 ) 



broods ill Japan are the reverse of the differences in colonr between the sniunier and 

 spring broods of machaon in Europe ; he will see that in Japan the black colonr has 

 considerably increased in the summer specimens, while in Europe the black colour 

 has decreased in the summer brood — a phenomenon which will make it evident at 

 once (1) that, if heat is (as maintained b_v Eimer and others) the factor which produces 

 the characters of the summer broods, the action of tlie same factor has opposite 

 results in these forms of machaon, which means that difference in colonr is not a good 

 measure of relationship, or (2) that the factor or factors which produce the characters 

 of the snmmer brood in Japan are different from the factors to which in Europe the 

 summer broods are due, which means that we do not know whether it is heat here 

 and some other factor in Japan, whether the reverse is true, or whether heat is at all 

 a prima causa of the characters of the snmmer broods. Works on Butterflies will 

 tell the student that transitional specimens between the ordinary and the black 

 fe.mnle of P. tui-nus* are recorded and are figured in Edwards, Butter/tics of Xorth 

 America, 2nd series, rapilio t. V. (1884), though it is said again and again in 

 Arthilduny that there are no such transitions, the absence of such transitional 

 individuals being again and again given as the main argument for the origin of 

 species per sulfiim.. Such and similar facts of importance we learn by looking over 

 the writings of entomologists. If the author of ArthiUlang had taken the trouble 

 to find out what was known to science about the Papilios which he selected for his 

 researches, he would not have considered in 1895 P. xnthus to be snbspecifically 

 distinct from xuthulus, as the summer form xuthus had already in 1875 been bred 

 from the spring form xuthulus, and as this has since repeatedly been done. The 

 case of xuthus and .ruthulus is, however, of significance in another respect. If 

 one knows that the small and the large, aberrant-looking, Japanese forms of machaon 

 stand in the relation of spring and summer broods to each other, the suggestion that 

 xuthulus and xuthus, which differ in a similar way, stand in the same relation must 

 present itself. If one has a material sufficiently large for the study of variation, 

 one must see that xuthus and xuthulus cannot be specifically distinct, as there are all 

 intergradations. If one compares the sexual organs of the very different specimens 

 of xuthus and xuthulus, suchKas were alone known to Eimer, one must become at least 

 doubtful that one has to do with diflerent subspecies or different species, as the sexual 

 organs do not show a distinguishing character, as species and marked subspecies do in 

 the case of Papilios with a more complicated structure of the male genital armature. 

 In Artbildum/ only the wing-pattern of xuthus is taken into consideration, and this did 

 obviously not show the author the true relation between xuthus and xuthulus. The 

 entomologist who knows that authors liave so often been deceived by the flexible 

 wing-pattern, and who has the case oi xuthus and xuthulus before him, will a priori 

 not be inclined to accept without further impiiry classificatory results which are 

 based only on the comparison of wing-patterns, though he reads in Arthildung I. 

 p. 23, " The main point, liowever, is, that by my researches the principal traits of the 

 real relationshi]) of the forms are determined, and that thereby a handle is given to 

 make the ' system ' in our branch of zoology what it really should be, the 

 expression of blood-relationship " ; and in II. p. 6C : " Whoever will dispute after 

 the appearance of my work, that the pattern is the most essential and the most 

 infallible guide for the recognition of the relationship of the Butterflies and for the 

 understanding of the laws thatl govern the origin of species, must necessarily have 



• The oklcst name is glaucns, but I use throughout this icjoiudcr the name of tiirniis, in oitler to 

 avoid confusion. 



