310 Dr. T. A. Chapman on a neiv form of seasonal 



He says " I find two very distinct forms of scale according 

 as I examine the thersitesAooking insects, or the undoubted 

 icarus specimens. The icanis scales seem to me to be 

 longer with straighter lateral margins, with the rows of 

 spots much closer together; these rows, too, seem to 

 extend nearer to the proximal end of the scale. In the 

 specimens I take for thersites the scales are shorter, the 

 lateral margins more rounded and the row^s of spots 

 further apart, and ending further from the proximal end; 

 that is to say, leaving a larger triangular space without 

 spots and giving the whole scale a much more transparent 

 facies than in icarus. All this agrees well with your 

 figures and description, but I have not been able to find 

 that the general number of rows for thersites is 4 or 5, 

 though for icarus it is certainly 5 or 6. It may be from 

 a difference in the part of the wing from which I have 

 taken the scales or from a difference in the race of thersites 

 here, or perhaps even they are not thersites at all; but I 

 find a large number of scales with 6 or 7 rows, almost 

 identical with what I find in escheri." 



Mr. Ball sent me certain specimens for examination ; 

 they were undoubtedly thersites in every respect except these 

 escheri-\ike androconia. 



There was also the habitat, which was further North 

 than I had supposed thersites to inhabit. 



This extended Northern range led me to suppose that in 

 Belgium the species must be single-brooded (monogeneutic). 

 I had already at Le Lautaret (7000 ft.) found a single-brooded 

 race of A. thersites in a locality that extended its range in 

 elevation to an equivalent to a northern latitude perhaps 

 even greater than that of Belgium. It occurred to me to 

 examine some of my Lautaret specimens, and I was at once 

 pleased and puzzled to find that they possessed the same 

 escheri-\ike androconia that Mr. Ball described. Examples 

 captured and flying at practically the same date at Bourg 

 d'Oisans, down the valley only some 20 miles from Lautaret, 

 had what I held to be typical A. thersites androconia. 



Had we then two species, flying so nearly together, 

 and undistinguishable except by the androconia ? Though 

 this seemed rather absurd, still, in view of the closeness 

 of A. thersites to P. icarus, it could not be dismissed as 

 impossible. 



It then occurred to me that at Le Lautaret I had, for 

 some reason, regarded the brood there as corresponding to 



