69 



for intense colour has been added. The other colour variation is of 

 the rarest occurrence, in fact I can find only one example. This is 

 with the red spots and red of hindwing changed to silvery white, 

 the darker portions of the wings and body being normal. It is diffi- 

 cult to account for this form, but perhaps the following may be 

 suggestive. This aberration occurred on the same ground as the 

 black ones, and one cannot but think that without the melanic form 

 the white could not occur, and therefore is an aberrant form of an 

 aberration. When a red loses the factor for intense colour the result 

 is yellow, when a factor for additional colour is added to the normal 

 red the result is brown or black ; if in turn the factor for additional 

 colour is eliminated from the melanic form, it seems reasonable to 

 suppose that, owing to the change that has taken place in the pig- 

 ment, the result would be white. I had hoped to test this theory by 

 breedmg from this white $ , but it was impossible to obtain the pair- 

 ing ; the melanic form is lethargic, and it is extremely rare to see 

 one on the wing even on the hottest day. Also it is quite different 

 in its resting position from the type, which sits with its wings laid 

 tightly along the body ; whereas the melanic form sits with its wings 

 spread, much after the manner of a Lycaenid sunning itself. The 

 white one remained for over a week refusing to move, even if placed 

 in the sun, and seemed quite devoid of sexual attraction. JVIales 

 would walk over her without exhibiting any interest, although this 

 was the only female in the cage, with at least a dozen males. 



The next type of variation to be considered is in the spotting of 

 the forewings, and in this respect the Zygaenas may be grouped as 

 follows : — 



With six spots as in filipendidae. 



With five spots as in lonicerae. 



With three blotches as in cnvieri. 



With four spots with the 5th and 6th joined together as in 

 acJiilleat'. 



With five spots and a lunular blotch as in camioUca. 



And with the spots confluent as in txirpnralis. 



In the five- and six-spotted forms the spots may coalesce in the 

 following manner : 1 and 2, 3 and 4, 5 and 6, or with any combina- 

 tion of these spots, and in extreme forms the confluence may extend 

 over the whole surface of the forewings, as in riibiciindiis, an ex- 

 tremely local form found in Italy. Speaking generally, the varia- 

 tion of the group is limited, and the same type runs through the 

 whole genus, and this feature, together with the slight difterence 

 between the various species, makes the family very complicated and 

 the species difficult to differentiate, an examination of the genital 

 organs giving little satisfaction owing to their similarity. 



Again, a certain race of a species may vary in a certain direction to 

 such an extent that it strongly resembles a distinct species, so that 

 differentiation with any certainty is almost impossible. Instances 



