EXPERIMENTS IN HYBRIDIZATION AND TEMPERATURE. 79 



the middle of June pupated, and during the same month pro- 

 duced imagines, which were one and all males (PI. IV. fig. 14). 

 These crossed back with anachoreta ? produced, at the beginning 

 of August, a further imaginal generation, but again only males ; 

 all the female pupae of this secondary hybrid hybernated. The 

 secondary hybrid males and, as has been since found, also the 

 females are much nearer to P. anachoreta, but, by exact com- 

 parison, differ in a regular manner from the last-named species, 

 especially in the reduction of the group of dark spots at the 

 dorsal angle of the upper side of the fore wings. The above- 

 mentioned secondary hybrid males were again paired with 

 anachoreta ? , and produced offspring, which, however, on 

 account of press of other work, were sleeved out, and not noted 

 further. 14 



The minority of the primary hybrid larvae of the crossing — 

 P. curtula (? X P. anachoreta ? — developed very slowly, and in a 

 somewhat different physiognomical form to the first series ; 

 whereas the former was an intermediate form, which stood 

 nearest to the phylogenetically oldest form, curtula, but which, 

 however, had distinct traces of its anachoreta origin ; the slow 

 developing larvae obtained more and more the characters of pure 

 curtula larvae. On Aug. 15th, 1897, when the offspring of nephews 

 — obtained from the other portion of the brood, which, however, 

 were treated in exactly the same manner — were in the larval 

 stage, not a single one of this second series had pupated, and 

 only two individuals were nearly full grown, which were much 

 larger than a big, full-grown anachoreta larva. One of these two 

 individuals pupated on the 21st, and the other on the 23rd of 

 August; both were females. 1^ All the remaining specimens of 

 this series would no doubt have been females, but they all died 

 during my absence from Zurich. During this time the imagines 

 had also emerged from the two pupae obtained ; I found them at 

 the beginning of October still alive, but knocked to pieces ; they 

 were, as far as could be seen from their condition, mostly related 

 in form to the phylogenetic oldest of the parent species. Both 



^* In the autumn of 1898 a small number of imagines of this pairing, 

 No. 30 (see Table, No. 15), were reared. They resulted entii-ely in male 

 specimens, which differed very little from P. anachoreta. These males were, 

 without doubt, capable of reproduction, although in a lesser degree. 



^5 Of two fLirther female pupse of this interesting hybrid from 1898 — 

 which I have named P. hybr. rceschkei, after my assistant, E. F. Raeschke, 

 who has rendered me great assistance in my experimental entomological 

 work during the last few years — one iinago emerged in October, and the 

 other died during the winter. The imago bred in October, 1898, is illustrated 

 (PI. IV. fig. 13). It shows the immense size of this female hybrid. This 

 female is, however, not so closely allied to the type of cm-tula as the two 

 individuals bred in 1897, which unfortunately escaped. The capabilities of 

 development of the eggs of this female could not be ascertained this time, as 

 not a single Pygcera male, either of hybrid or pure origin, was present at 

 that time, 



