J. W. H. Harrison 3 



as well as the attachment of the former to Lyda. Nevertheless, many 

 additional points in which P. rachelae and P. lapponaria resemble Nyssia 

 zonaria — like the larger ova, the indistinct larval pattern, the delicate 

 texture of the larval skin, the shape of the wings of the imago — demon- 

 strate that the lapponaria-rachelae pair although, as we gleaned above, 

 veritable members of the genus Poecilopsis, are truly transitional between 

 their congeners and Nyssia. So, too, the agreement in the ova, larval 

 pattern and pupae between L. hirtaria, P. pomonaria, and P. isahellae, 

 emphasised in no uncertain way by the fertility of the hybrids between 

 them, proves that the last two are derivatives of L. hirtaria. 



To sum up our facts, we are now in a position to state that the 

 genus Lycia has yielded Poecilopsis, which in turn, via the species 

 P. rachelae and P. lapponaria, has given rise to Nyssia, although the 

 exact relationship of all the species within the three genera has not been 

 stated. This need not detain us long. L. ursaria and L. hirtaria are 

 what are termed " representative " species, i.e. are forms not widely 

 apart, evolved from two sections of the same original, severed by some 

 geographical accident or incident, ursaria from its pattern being nearer 

 the early form. P. rachelae and P. lapponaria are likewise the isolated 

 fragments of a Preglacial speciess thrust apart by the pressure of the 

 oncoming ice as the Glacial period moved to its climax. On the con- 

 trary, that P. pomonaria and P. isahellae have diverged in more modern 

 times, and that P. pomonaria is the older, are indicated by the complete 

 fertility of their hybrids, by the superior fertility of the hybrids between 

 hirtaria and pomonaria over the corresponding hirtaria-isahella hybrid, 

 and by the attachment of P. isahellae to larch {Larix deciduc^ — a Post- 

 glacial immigrant into Europe. Nyssia alpina, N. graecaria and N. 

 italica bear a somewhat similar relationship to N. zonaria, having arisen 

 in a common offshoot of that species subsequently split by isolation due 

 to glacial action into the present assemblage. 



Very briefly in this way a phylogenetic tree such as appears in 

 No. Ill of the present series of papers has been worked out, and since 

 it has been given there it need not be repeated. 



For ease in reference, before the discussion is given, details of the 

 sex results must be summarised, and they appear in the classified tables 

 below. 



1—2 



