234 Hybrids of Bistonine Moths 



above, is carried through both generations this would explain the 

 difference in form between two hybrids so nearly the same in blood, 

 both being three quarters hirtaria and one quarter pomonaHa. 



PART 11. ON THE CHROMOSOMES IN GAMETOGENESIS 

 OF THE MOTHS LYCIA {BISTON) HIRTARIA AND 

 ITHYSIA {NYSSIA) ZONARIA, AND IN THEIR HYBRIDS. 



By L. DoNCASTER, Sc.D., 

 Felloiv of King's College, Cambridge. 



The work of which this paper gives a preliminary account was 

 undertaken to find out, if possible, any cytological cause for the fact 

 that reciprocal crosses of Lycia (Biston) hirtaria and Ithysia (Nyssia) 

 zonaria give different results as regards the sexes of the offspring. 

 Mr J. W. H. Harrison, who very kindly supplied me with the hybrid 

 material used, has described the results of the two crosses, together with 

 other hybrids, between species of the same genera. For the present 

 purpose the important facts are that the cross zonaria J x hirtaria </ 

 produces only male offspring, resembling zonaria somewhat more nearly 

 than hirtaria) hirtaria J x zonaria </ gives both sexes, with a con- 

 spicuous excess of females (more than 2 $ $ : 1 ^). The males of this 

 second cross are not strikingly different from those of the converse cross ; 

 the females are remarkable in having small flightless wings. (Plate 

 XVII.) The wings of the hirtaria J are of normal size and are capable 

 of flight ; those of zonaria are vestigial, so that in this respect the hybrid 

 is intermediate \ 



Although the observations which I have been able to make on the 

 small supply of material hitherto available have not led to very satis- 

 factory results with regard to cause of the difference in sex-determination 

 in the reciprocal crosses, the general behaviour of the chromosomes in 

 the gametogenesis of the hybrids is so remarkable that I think it worth 

 while to publish an account of it at once. The chromosomes of the two 

 species are very different from one another, and in the hybrids most of 

 the chromosomes derived from each parent can be recognised at a 

 glance. 



1 It should be noted that the reduction of the wings, which is a secondary sexual 

 character of zonaria, is transmitted by the zonaria male. 



