SOMATIC MOSAICS IN LEPIDOPi'EKA. 105 



17. ab. andersoni, n.ab. 



This is a very remarkable aberration by reason of the extensive 

 confluence of spots 3 + 1+2 + 4 + 5, the only isolate spot being 

 No. 6, which is large. The scutellar spot is present. 



Also taken at Njoro, B.E.A., by Mr. T. -J. Anderson. 



Type in General Collection of the Nat. Hist. Museum, S. Kensing- 

 ton (1911,384). 



Formula: 3 + 1 + 2 + 4 + 5, 6, ^. 



18. ab. hlairi, n.ab. 



This aberration with thirteen spots is a very striking one, in view 

 as well of the two bold confluences of spots 2 + 1+3 and 4 + 5, as 

 of its entirely black thorax. In this latter respect it is, so far as I can 

 trace, unique, and the antithesis of ab. albicolUx, Chobaut, with its 

 white thorax. 



In this aberration the only isolate spots are Nos. 6 and i. 



I have with his permission named this aberration after Mr. K. G. 

 Blair, B.iSc, F.E.S., of the Natural History Museum, S. Kensington, 

 as a slight acknowledgment of his invaluable help, while I have been 

 working at the Museum on this species. 



Taken at Njoro, B.E.A., by Mr. T. J. Anderson. 



Type in General Collection of the Nat. Hist. Museum, S. Kensing- 

 ton (1911,384). 



Fokmula: 2 + 1 + 3, 4 + 5, 6, ^. 



Somatic Mosaics in Lepidoptera. 



By E. A. COCKAYNE, M.D., F.E.S, 



In August, 1917, Mr. H. B. Williams obtained a pupa of Vanessa ia, 

 L., at Holmwood, the two sides of which were different in colour. He 

 has kindly given me the pupa-case, the imago, which emerged from it, 

 and a photograph he took before emergence. The division between 

 the two colours is quite sharp and runs exactly along the middle line. 

 The pupal skin of the right side is darker in colour and covered with a 

 tine dark reticular pattern, that of the left side is pale and only shows 

 faint indications of the reticular pattern; the dorsal spines of the right 

 side are deeply pigmented down to their bases, those of the left are only 

 pigmented at the tip. The imago which emerged appeared to be a 

 female, and the wings showed no difl'erence in colour or pattern on the 

 two sides. Its only abnormality was a slight crumpling of the posterior 

 border. The palpi and antennae were of equal length. 



Dissection of the dried abdomen was fairly successful. Both ovaries 

 were identified, as were the cement glands, the ductus burs^e and the 

 bursa copulatrix. The spermatheca were broken. The external geni- 

 talia were normal and female. There was no contrast in the surround- 

 ings, in which the larva pupated, nor do I know of any evidence that in 

 a larva susceptible to its surroundings during pupation a dark back- 

 ground on one side and alight one on the other will produce a difl'erence 

 in colour on the two sides of the pupa. 



I think it belongs to the group which I described in the JoumaL of 

 Genetics, 1915, v., p. 87, under the name " Heterochroism." Had the 

 species been a more variable one the imago also might have shown a 

 difference in colour on the two sides. 



