E. J, Allen and E. W. Sexton 349 



before the female died. Her last broods had eyes of very dilute red, 

 pale pink in some, and pale yellow in others, but these, after moulting, 

 all became bright red. 



Adult specimens are sometimes met with, the eyes of which have 

 very dark pigment in the centre and bright red round ; sometimes after 

 moulting the eyes are bright red, more rarely they remain unchanged. 

 Only three young have been recorded from the red stock with eyes at birth 

 so dark as to appear black. Two died soon after extrusion, but the 

 third came to maturity, a male, and its eyes were then red with dark 

 centres. It was mated with a female with similar eyes and had numer- 

 ous offspring all with the normal bright red colour. 



II. Absence of Colour associated with Imperfect Form. 



A second mutation appeared in the F2 generation from a cross 

 between Pure Black and Pure Red. Out of a brood of 12, 8 had normal 

 eyes, 7 Black and 1 Red, the remaining 4 were what we call the 

 "Albino " eyes (Plate XIV, Fig. 3). 



The Imperfect Form differs from the Perfect or Normal in shape. 

 which varies with the individual, and even in the same individual ; in 

 the margin, which is always irregular and ragged in outline, and generally 

 deeply indented and broken up ; in the number of the ommatidia, which 

 are always few in number, never reaching to even half the number in the 

 normal ; in the size and shape of the lenses of the ommatidia, which are 

 always variable ; in the disposition of the ivhite pigment, which is not 

 spread evenly between the ommatidia as in the normal, but appears as 

 masses or patches of white with the ommatidia scattered here and there 

 in no sort of regularity, frequently with some lying beyond the margin 

 of the ommateum, quite apart from the pigment. 



The principal difference between the two forms lies in the Absence 

 of Retinal Colour, and this character is always found associated with 

 the Imperfect shape of the eye. 



The Perfect Form with Colour is dominant to the Imperfect Form 

 without Colour (i.e. Albino) giving F^ in the proportion 3 : 1. 



The Albino eyes all carry the factor for Colour, some the factor for 

 Pure Black, others the factors for Black and Red, and others again for 

 Pure Red, but, unless mated with Colour, their constitution cannot be 

 ascertained. Mated together, they give Albinos. 



Only once, in the whole course of the experiments, has an instance 

 occun-ed in which two degenerate Albino-eyed animals produced a normal 



