E. J. Allen and E. W. Sexton 351 



No-white ; or, as in an instance referred to later, the young may be 

 hatched with the white pigment apparently normal, and yet suffer 

 a gradual reduction of it until at maturity they are either practically or 

 completely No-white. 



Some of the experiments are mentioned below in order to show these 

 distinctions. 



(a) The first record of the sudden appearance of a No-white was 

 in November, 1914, in the F^ descendants of one of the crosses made 

 between the Pure Black and the Pure Red strains, which had been kept 

 under laboratory conditions for two and a half years, since June, 1912. 



In all, .5596 F^ young were hatched during the period September, 

 1914 to September, 1915, and among these 3 typical No-whites 

 appeared, and 13 one-sided No- whites (i.e. one eye with normal white 

 reticulation and one No-white). 



Some similar experiments have been described in a previous paper, 

 Allen and Sexton, 1917, pp. 326-330, and 336-341, which see also 

 for one-sided No-white matings with normal-eyed animals (p. 339). 



(6) The following experiment illustrates the gradual development 

 of No- white. 



Two animals were taken from the Pure Black normal-eyed stock 

 brought in, February, 1915 (Pair V, see p. 329, Allen and Sexton, 1917, 

 Journ. M.B.A., xi.). The eyes of the male were normal, while those of 

 the female had less white pigment than usual. One of the F^ generation, 

 a male, had very thin reticulation in its eyes ; it was mated with a 

 female of the same brood, one brood of 13 was hatched, and then it ate 

 her — ^before her eyes had been examined. Of this brood, extruded 

 November 15, 1915, 11 had thin reticulation, and the remaining two 

 were typical No-whites. These were left to interbreed, and examined 

 at intervals. In September, 1917, 12 young were seen, 10 practically 

 normal-eyed, and the two which were separated for this experiment and 

 kept under daily observation. 



These were, a male with very little white in the eyes, and a female 

 with the Right eye No-white, and regular but very thin reticulation in the 

 Left eye, and a tiny deep spot on the left side of the head (i.e. three eyes 

 with thin reticulation and one eye No-white). 



The experiment gave an unexpected result. 311 young in all were 

 hatched, all except two with perfectly normal eyes, eight of them with 

 more white than usual and 170 "spotted" as well. (The two exceptions 

 each had one eye No-white.) But by the time they reached maturity 

 the white pigment had either vanished altogether or become reduced 



Journ. of Gen. ix. 23 



