276 Genetical Studies in Moths 



have been brought about either by a lack of physiological affinity 

 between the possible parents or by a failure to copulate, the former 

 being the more likely explanation, so readily do the Oporahia species 

 cross pair. 



The Gross between dilutata $ and the F^ Male. 



This mating proved, for this set of experiments, a very conspicuous 

 success, for no fewer than 73 fertile ova were laid in the interstices of 

 the muslin cage and hatched in March 1918. I offered them the usual 

 pabulum employed by me, i.e. Crataegus oxyacantha, and this, as with 

 all other Oporahia, hybrid or pure, was instantly accepted. All of the 

 little larvae reached the second instar, when I began to lose a few. 

 Still, in the end, 46 pupated. 



These larvae were gorgeous creatures and far surpassed the magnifi- 

 cent caterpillars of the two dilutata- autumnata crosses. They possessed 

 the beautiful green ground with the yellow bands and dorsal red blotches 

 of those forms combined with a darker, olive green shading derived 

 from filigrammaria — the whole scheme of colouration contrasting so as 

 to yield a very striking effect. In the possession of this rich garb the 

 larvae showed the presence of the three contributing forms autumnata, 

 filigrammaria and dilutata. 



They went to earth and span cocoons in no wise unlike those of 

 their congeners, and every single larva produced a fine healthy pupa 

 which remained alive until late in August when the maturation divisions 

 ought to have been proceeding. Then the fatal want of viability so 

 often the bane of hybrid pupae in the production of which dilutata 

 females have taken part exerted its influence, and every pupa died, just 

 as is one's experience, with but rare exceptions, in the crosses referred to. 

 Fortunately enough, to a careful observer the determination of the sex 

 of pupae, even of small Geometrid pupae like these, presents no great 

 difficulty, and it was readily ascertained that all of the 46 pupae 

 were males — a result entirely in agreement with the composition of 

 ordinary broods reared as the outcome of a pairing between dilutata % 

 and autumnata cf. This observation determines that, in the power of 

 the male sex gene, there is no significant difference between any derived 

 from the F^ ^ ^ and those of pure autumnata. 



The Pairing o/ filigrammaria $ and dilutata ^Z". 



Ova of this parentage were obtained with equal facility, but the 

 number of salmon pink ones noted when the cage was opened only 

 amounted to 19 out of 97. Clearly the pairing had been a success, but 



