OCR Text |
Show 1906.] BREEDING EXPERIMENTS WITH LEPTDOPTERA. 129 It may be pointed out that this case is so like what is known of some other instances of alternative inheritance in moths, e. g. in Amphidasis betularia and its var. doubledayaria, that it will probably be found that these also are simple cases of Mendelian inheritance. II.-ABRAXAS GROSSULARIATA. (Experiments by the Rev. G. H . Raynor.) We now turn to the case of A braxas grossulariata and its var. lacticolor (flavofasciata). Mr. Raynor obtained, some years ago, a rare variety of the female, in which the black markings are very much reduced and assume a partially linear form. They are also characterised by their indefiniteness of outline ; instead of the sharp edge to the black marks which is characteristic of the type, in var. lacticolor the black spots have an indefinite appearance, which makes them appear to have been put on with a nearly dry brush. The only exception to this rule is the spot in the centre of the fore wing, which is more conspicuous than in the type (see PI. VIII. figs. 4 & 5). The var. lacticolor may therefore be regarded as resembling an albino, in which the black pigment is reduced to a constant extent, but not quite absent. The yellow bands do not differ from those of the type. It should be mentioned that the amount of black varies very widely in the type, but at its most extreme reduction the insect does not resemble lacticolor, since the spots are small and definite. Among the many thousand insects bred by Mr. Raynor, no intermediate between lacticolor and the type has occurred. W h e n the original lacticolor 2 w a s paired with a normal $ , all the offspring were normal. When, howTever, two of the progeny of such matings were paired together, some of the female offspring-were lacticolor, but the var. did not occur among the males (Table VIII.). A number of such families were reared which are not included in the tables, since the numbers were at first not recorded. It appeared, however, that the var. lacticolor is a Mendelian recessive of quite a new type, since it was known only in the female, and more exact experiments were undertaken to investigate it further. In 1903, in addition to pairings of the type D R X D R (first crosses paired together), lacticolor 2 s were paired with heterozygous tfs (see Table IX.). The result of these matings was that lacticolor appeared in both sexes, some of the 6 s and some 2 s being lacticolor, others of each sex normal. Some of the males used as fathers in these experiments were first crosses, others were heterozygous males of the second geneiation, which had lacticolor sisters. One F2 male (exp. xliv. '03), which had two lacticolor grandparents, when paired with a lacticolor 2 had onty normal offspring, showing that in F2 pure dominant males occur, in addition to heterozygotes, as is expected on the Mendelian theory. P R O C ZOOL. Sec-1906, VOL. I. No. IX. 9 |