STUDY OF VARIATION IN THE RACES OF ZYGAENA FILIPENDULAE, L. 83 



or, in other words, two sub-species, as compared with each other. I 

 think the above evidences are more than enough to show that real 

 transition exists between them. This brings me to speak of a 

 phenomenon, which is more frequent in the genus Zygaena than in 

 most other genera, and which constitutes one of the chief difficulties 

 one meets in dealing with them. My experience in the matter has 

 evidently been shared by two of the cleverest Lepidopterists, Tutt and 

 Oberthiir. " I do not doubt that the rest have gone through it, but, as 

 their writings consist in catalogues with short formal descriptions, 

 they have carefully avoided acquainting us with their difficulties by 

 not giving any explanation and justification of many doubtful general 

 conclusions. Individual variation is, as a rule, very extensive in the 

 Zygaena, and in some species and races particularly, it produces 

 differences of aspect far greater than are several of the specific ones 

 compared with each other ; in nearly all the species, however, 

 characteristic and individual variation follow most definite plans and 

 are quite similar throughout the genus. The result of this is that 

 several species resemble each other very much, races and individuals 

 being produced which resemble kindred species more than they do the 

 other more usual races and individuals of their own. When two 

 species of this sort are found in the same locality and one sets to work 

 to separate a series of specimens, part of them are easily grouped into 

 two sets, but the remainder, to all appearance, constitute a continuous 

 series of transitions from one to the other, in which no break is 

 discernible. These apparent transitions were in the past 

 explained in a wholesale fashion by the very convenient " hybrid 

 theory," and entomologists, at this, set their minds at ease about them. 

 With the increase of knowledge this theory has steadily, been losing 

 ground, and I think I can now safely state, that it only survives in 

 the minds of those who are not sufficiently acquainted with this genus. 

 No one has certainly ever collected as many Zygaena as Querci in his 

 forty years' experience in Italy, and yet neither he nor I in tens of 

 thousands of specimens examined have ever been able to detect one of 

 these precious monsters, in spite of the fact that pairing between 

 different species was several times observed in nature both by him and 

 by myself. The counterpart of this negative evidence is to be found 

 in the fact that specimens, identical with the most tempting ones 

 collected, where two species occurred together, were also found as 

 extreme variations in series collected in localities, where only one of 

 the two existed. These examples have been chiefly afforded by 

 filipendulae and lonicerae, which have proved treacherous even to the 

 most experienced. In 1899 we still find Tutt utterly bewildered in 

 his attempt to make out the Zygaena species. His chapter on the 

 " Anthrocerid species " at the end of vol. I. of the Brit. Lepid. is most 

 interesting and instructive, for it shows what difficulties one meets 

 with when one tries to see one's way through " this unwieldy 

 genus," as he puts it, even if one resorts, with the greatest 

 accuracy, to a study of the early stages and of the structure 

 of each insect. Tutt's brain-power was wonderful in the most 

 minute systematic analysis and in patiently collecting and classi- 

 fying every possible information upon a subject, but it evidently 

 exhausted itself in this particular direction ; he rarely drew enlightening 

 conclusions from his long labour ; that evidently is why he failed here, 



