9 



ject : — Ticniocamija stabilis male and T. gothica female (' Ent,,' xxi., 

 p. 158); Cerastis vaccinii male and Miselia oxijacantha: female (Inc. 

 cit., p. 188); Xylophasia iiionn(jlt/pIia male and Hailena trifoUi female 

 (/of. cit., p. 282); Melitaa athalia male and Polijgonia c-albmn female 

 (Schneider, 'Iris,' xix., p. 107) ; Aglak urticic male and Epinephele 

 janira female (' Ent.,' xxxiii., p. 224) ; Melitaa cyiithia male and 

 Erehia lappona female (Rebel, ' Societas Entomologica,' ii., p. 73) ; 

 Attacus cecropia male and Sphinx ligastn female ('Ent.,' xix., p. 136); 

 Drt/as paplua male and Varnassins a polio female (this I saw myself 

 at Faido, in the Leventina, in company with Mr. Warren) ; Salamis 

 anacaidii male and Aphelia apollinaris female (Trimen, ' Proc. Ent. 

 Soc. Lond.,' 1880, pp. 23, 24, the moth being a day-flier, and bear- 

 ing a general resemblance to the butterfly) ; Enchloe canhnrines 

 male and Bapta temerata female (' Ent.,' xxi., p. 188 — here there is 

 no such excuse)." 



After admitting the probable infertility of any such pairings 

 (except the two Tt^niocampids) I added: — "The very important 

 fact still remains that it is not the differences of the structures in 

 question which per se are the cause of the infertility, as they could 

 only produce this effect directly by making pairing itself impossible, 

 and at the most they can only be a secondary and correlated cause, 

 not to be compared in importance with such facts as species appear- 

 ing at different times, inhabiting different altitudes or latitudes, 

 feeding on different (or at any rate unrelated) food plants, hibernat- 

 ing at a different stage of existence, flying at a different time of day, 

 or possessing any other habit which must either effectually keep 

 them apart, or be practically certain to cause the early death of any 

 hybrid progeny which might manage to struggle into existence." 



And again a little further on : — " I do not believe their phylo- 

 genetic and consequent classificatory importance to be nearly so 

 great as that of many points in the earlier, especially the egg and 

 newly-hatched larval, stages; as these seam, to some extent at any 

 rate, to recapitulate the evolutionary history of species, genera, etc., 

 or at least to point the way to a partial reconstruction of such 

 history. 



" But putting all this aside, and granting for the sake of argu- 

 ment that this is the most important— nay, far the most important 

 — of all structural differences, it is still liable to abuse ; for it can- 

 not for a moment be conceded (or even claimed) that this is the 

 onli/ mode of divergence, and parallel differences in this respect may 

 have been evolved after other divergences had taken place, the 

 dormant tendency having been retained, and we might thus find 

 parallel groups exhibiting the same different forms of clasp, etc., 

 even when these groups had in other respects diverged somewhat 

 widely from each other ; and, on the other hand, likenesses, or even 

 identity of structure, in this respect might be retained, especially in 

 closely related species, even after they were specifically separated by 

 differences of habit, food-plant, habitat, etc. In the first case we 



