52 



quite another matter from a thickening of the end of the same 

 stripe such as is seen in MacJiaon. In fig. 5 the apex of the pear- 

 shaped pupil hits the rim in the middle of the outer side of the 

 ocellus and the rim is prolonged beyond the connection. I call at- 

 tention to this last point also, for these little things have a mean- 

 ing. In MacJiaon the end of th^ rim or stripe is thickened on the 

 side farthest from base, and this end is 90*^ to 150*^ further round 

 the circle than the end of same stripe in Zolicaon. 



Now, how came that pupilled ocellus to be a main feature of 

 of Zi?//(r<fr^;/, and a blind ocellus of J/(^r/^^<?;^ .^ If Zolicaon is de- 

 rived from MacJiaon, as Dr. Hagen declares, but cannot prove, 

 how came in that persistent pupil, not found in the parent form? 

 On the other hand, if MacJiaon is derived from Zolicaon, and, 

 while guessing prevails, that guess is as good as the other, why- 

 do not examples of reversion occur? Why do we merely see a 

 thickening of the end of the rim of the circle in MacJiaon, if there 

 is any change at at all from a mere line, and never a pupil? 



Without question, every mark on a butterfly wing is variable, 

 and among thousands of examples of a given species, all sorts of 

 varieties might be expected, but ivitJiin certain limits. Something 

 cannot come from nothing, there must be a point or mark, a line 

 to base a variation on. A line may break into spots, or spots 

 may coalesce into a line or band, or bands, by suffusion, may 

 spread all over the surface of the wing. But we never need hope 

 to find in any sport an entirely new mark on a clear ground. 

 There will be no ocellus on Callidryas Eubnle. Now, I know of 

 no evidence that a pupil was ever seen on the fulvous spot in 

 MacJiaon. If such an example had occurred every collector 

 would have regarded it as a singularity. It would have been 

 treasured, for all collectors are eager to secure any oddity, and, 

 probably, an account of it would have reached one of the ento- 

 mological journals. In which case, Dr. Hagen, who knows all 

 about the literature of entomology, would certainly have seized 

 upon it and made it conspicuous in his paper. He has discovered 

 two instances in MacJiaon of a cell more or less black ; one in a 

 figure by Freyer, " which has the basal part of cell black, except 

 a small paler spot near the base," p. 155 ; and one in a dwarfed 

 butterfly in the Cambridge Museum, from Switzeland, "which 

 has the basal half of cell black. That he say's nothing of variation 

 ■which shows a pupilled ocellus is the best proof possible that no 

 instance of it is recorded, at least. If, however, such an ocellus 

 ever did appear in MacJiaon, it would fall under what Darwin calls 

 the law of analogous variation, where " varieties of one species 

 mock distinct but allied species," to be explained on the " prin- 

 ciple of allied species having'descended from one primitive form." 

 That is, it would be a case of reversion. 



I think it highly probable, from various reasons, especially 

 from the peculiarities of the caterpillar in its several stages and 



