Several autosomal mutations had been found in which the facets of the compound eye are disarranged. One that was sex-linked appeared in February 1914. Under the low power of the binocular microscope the facets are seen to be irregular in arrangement, instead of being arranged in a strictly regular pattern. The ommatidia are more nearly circular than hexagonal in outline, and are variable in size, some being considerably larger than normal. The large ones are also darker than {76} the smaller, giving a blotched appearance to the eye. The short hairs between the facets point in all directions instead of radially, as in the normal eye. The irregular reflection breaks up the dark fleck which is characteristic of the normal eye. The shape of the eye differs somewhat from the normal; it is more convex, smaller, and is encircled by a narrow rim destitute of ommatidia. Facet arose in a back-cross to test the independence of speck (second chromosome) and maroon (third chromosome). One of the cultures produced, among the first males to hatch, some males which showed the facet disarrangement. None of the females showed this character. The complete output was that typical of a female heterozygous for a recessive sex-linked character: not-facet [female] [female] (2), 112; not-facet [male] [male] (1), 57; facet [male] [male] (1), 51. Of the three characters which were shown by the F_2 males, one, facet, is sex-linked, another, speck, is in the second chromosome, and maroon is in the third chromosome. All eight F_2 classes are therefore expected to be equal in size, and each pair of characters should show free assortment, that is, 50 per cent. The assortment value for facet speck is 48, for speck maroon 52, and for facet maroon 48, as calculated from the F_2 males of table 58. TABLE 58.--_P_1 speck maroon_ [male] x _wild_ [female] [female]. _B.C. F_1 wild-type_ [female] x _speck maroon_ [male]. +----------+----------------------------+ | | F_2 females. | |Reference.+-------+-----+------+-------+ | |Speck |Wild-|Speck.|Maroon.| | |maroon.|type.| | ~ | | | | | ~ +----------+-------+-----+------+-------+ | 66 | 31 | 30 | 26 | 25 | +----------+-------+-----+------+-------+ +----------------------------------------------------------+ | F_2 males. | +------+-------+-------+-----+-------+------+------+-------+ |Facet.|Speck |Facet |Wild-|Facet |Speck.|Facet |Maroon.| ~ |maroon.|speck |type.|maroon.| |speck.| | ~ | |maroon.| | | | | | +------+-------+-------+-----+-------+------+------+-------+ | 14 | 14 | 14 | 10 | 11 | 17 | 12 | 17 | +------+-------+-------+-----+-------+------+------+-------+ LINKAGE OF FACET, VERMILION AND SABLE.