166 Dr. E. A. Cockayne on the condition of the scales 



Examined under a high power {^\- inch oil immersion) 

 it is seen that they are quite colourless by transmitted 

 light. The longitudinal ribs are present, though often 

 crinkled, but no cross striae are present with the excep- 

 tion of a few imperfect ones at the extreme base of the 

 scales. 



A few scales were found in which the lateral margins 

 were turned up, and in which very pale yellow dye was 

 present, but no cross striation. Unfortunately they were 

 mounted in balsam, and I could not see whether they 

 were blue by reflected light. If a scale of this nature 

 could be isolated and examined unmounted it would settle 

 the controversy as to the cause of the blue colour in the 

 blue liycaenids. 



Near the base of all four wings in both the specimens 

 examined, and along the costal margin of the right fore- 

 wing in one of them, normal thick blue scales were found 

 with the abnormal ones. 



Some of the scales on the fringes were thinner and more 

 hair-like than is usual, but the scales on the undersides of 

 the wings were all quite normal. The peculiarity can 

 scarcely be due to any pathological condition acting upon 

 the scales from without. If this w^ere so the neighbouring 

 dark scales and androconia would not escape, nor would 

 the scales of the underside be perfect. 



No injury, nor any infection by a pathogenic organism, 

 would be likely to affect the upper surfaces of all four 

 wings in the uniform and complete way in which it is 

 almost always affected in these leaden thetis. It is much 

 more likely to be dependent on some inborn error of 

 development. 



The following observations of Mr. G. T. Bethune-Baker 

 lend strong support to this view. According to this 

 author the blue scales in Polyommatus dolus var. vittata 

 are very similar to the abnormal scales of the aberration 

 of thetis. I quote the description of these in his Presi- 

 dential Address (Proc. Ent. Soc. 1913, p. clviii) : " An 

 extraordinary character, however, obtains in the ordinary 

 blue wing scales, the whole of which are curled round 

 so as to- form more or less short tubes; the process ap- 

 pears to be that each side of the scales turns over, and 

 occasionally they meet thus in the centre, but moi'e 

 generally one side will overlap the other and so form a 

 more or less perfect tube ; by this I mean that the basal 



