176 THE ENTOMOLOGIST. 
when thus retarded A produces A, entirely skipping B. The 
hypothesis of the learned Doctor was that both forms were 
descended from Pieris bryonia, an alpine single-brooded form, 
which perhaps existed over Europe during the glacial period 
(this species is very much darker than even the British spring 
form of the insect); that, as the climate became ameliorated, the 
insect gradually acquired the double-brooded habit, and at the 
same time became seasonably dimorphic, or, as I term it, 
horeomorphic. He then proceeded to test the truth of this 
hypothesis by forcing the insect back to its old condition of 
single-broodedness, and with the result that the form, that of the 
summer emergence, least like Pieris bryonie, was eliminated. 
All this is well set forth in Mr. Raphael Meldola’s translation of 
the Doctor’s work on this very interesting subject. Some of the 
British species of Hphyra and Ennomos amongst the moths, and 
of Lycena and Polyommatus amongst the butterflies, are horeo- 
morphic. EHnnomos illustraria is horeomorphic; and it has been 
observed that out of one brood some of them will appear in the 
summer in the form of the summer emergence, whilst others 
remain in the pupa state all through the winter, and appear the 
next spring with the characteristics of those of the spring 
emergence. Other species of the genus Hnnomos are equally 
marked in their horeomorphism. ‘This is perhaps the most 
interesting of all the forms of variation to which I have adverted. 
It is known to occur in several Kuropean butterflies. Araschnia 
prorsa has its horeomorphic form levana, and its intermediate 
form porima. In America it occurs in a true Papilio. Mr. 
Edwards, in his ‘ North American Butterflies,’ gives an account 
of exceedingly interesting results he had obtained in breeding 
this insect, known under the names of Papilio ajax, P. telemonides, 
and P. marcellus. This is a very complicated case, dimorphism 
and horeomorphism existing in the sume species. Mr. Edwards 
uses the old name of P. ajax to include all the variations; 
P. walshii, and its subvariety P. abbottii, for the spring emergence, 
and retains the name of P. telemonides for the intermediate form, 
and that of P. marcellus for those of the summer emergence. 
In conclusion I have to add that in each of the classes I 
could have given many more instances of the different conditions 
of variation, but I have restricted myself to a few cases only, 
which I deem sufficiently marked to illustrate the subject. 
