105 



Let us examine the spots of Z. transalpina. Six lovely crimson spots, 

 set in a framework of purple or green. What richer contrast can be 

 desired ! Six spots in three pairs, just as in the common Z. filipen- 

 dulce, and it would puzzle one to describe exactly in words how this 

 species differs from filipendidce. Yet it does differ from it, and very 

 considerably too. The deep brilliancy of its purple or green ground 

 colours, its bright crimson, the clear line of demarcation, almost as 

 if a dark line had been drawn around them, separating the spots 

 from the ground colour, mark this species off distinctly at once. 

 The basal pair of spots are both small ; the upper one occasionally 

 sends out just a little pointed spur, but this never reaches the length 

 which is normal in achillece, pilosell^z, or exulans, and which occurs 

 occasionally in our British Z. lonicerce. The middle pair of spots, 

 too, are very constant, both in size and position ; they are usually 

 well separated, but occasionally are closer together, but never 

 actually join ; the subcostal nervure always passes through the upper 

 spot, and is not restricted to the space below, as is usually the case 

 in some of its relatives. In the outer pair of spots, however, there 

 is considerable variation, and to them we must now pay a little 

 attention. 



You all know that occasionally our common six-spotted Burnet 

 (Z. filipendidce) produces an aberration, which has once or twice 

 been referred .to a form known on the Continent as ochsenheimeri. 

 This form has the sixth spot (the lower one of the outside pair) ill- 

 developed and smaller than usual ; but in filipendidce this character 

 is only of occasional occurrence, and is never present in all the 

 insects in any given locality ; it is very uncertain in its appearance, 

 and frequently does not occur in a district at all. Now, our 

 more modern ideas of the evolution of species have led us to 

 suppose that, given a large number of closely allied species, each 

 with normally constant characters, the various characters of the 

 allied species will occasionally appear as a chance reversion or sign 

 of progressive development in any of the species. We have Burnets 

 with five spots only, on both upper and under sides ; Burnets with 

 five spots on the upper and six on the under sides ; other Burnets 

 with five large and one (the lower of the outer pair) small spot on 

 both sides ; whilst others have six well-developed spots. We expect, 

 therefore, to find occasional specimens of any given species showing 

 the characters of the allied species, and so it is ; and it is these 

 tendencies to reversional (or developmental) aberration that present, 

 even to the most observant and best informed specialists, serious 

 difficulties oftentimes in correctly naming allied species. 



Now, Z. transalpina exhibits this tendency remarkably well. It is 

 a species with six spots, which are usually well developed ; but on 

 the other hand, in a fair percentage of its specimens, the sixth 

 spot is considerably less in size than is normally the case. From 

 Staudinger's " Catalog " it would appear that this is more usually 

 the case in some districts than in others, for, it seems that in many 



