SEASONAL POLYMORPHISM. 179 



exactly consists in the totality of the Po Basin ; the waterpartings of 

 svich mountain masses as the Alps to the north and west, and the 

 Apennines to the south, mark so sharply the limits of very different 

 climates, both northward and southward, that one is in no way 

 surprised at finding perfectly characterised and peculiar races in this 

 region. The climate is intermediate between that of Central Europe 

 and that found from Liguria and Tuscany downwards, and so are the 

 races of its Lepidoptera, which develop in incomparably damper sur- 

 roundings than those of the rest of Italy, and feed on a luxuriant green 

 vegetation, which does not get dried up during July and August. So 

 great is their resemblance to those of Central Europe that one might 

 very reasonably doubt whether the Po Basin should not be con- 

 sidered a subzone of the latter, rather than be joined to the rest of 

 Italy. The extent to which the Po Basin is occupied by the Alps, with 

 their numerous peculiar species and races, would be another strong 

 reason not to split the Alpine subzone. It is quite true that strictly 

 Alpine species of very high altitudes are, as a rule, similar on both 

 sides of the waterparting (except rare cases, like that of R. alecto, Hb., 

 on the Stelvio), but, on the other hand, there are two reasons which 

 make me conclude that the Po Basin should be separated from Central 

 Europe : one is that several species, characteristic of the latter zone, 

 stop short exactly at the waterparting of the Alps (so that they are 

 found, for instance, in North Tyrol, up to the Brenner Pass, and not 

 in South Tyrol), or only just cross it in a few localities (such are C. 

 palaemnn, C. ainphidavias, L. areas, S. pnini, C. chrt/sotheiiie, C. 

 luyniiiddjic, ('. Iiera, E. arete, H. arethiisa, M. matnrna, M. pa rtJienie {a,s 

 distinguished homM.raria), A. levana, P. l-alhiini, E. xant/wmclas; very 

 probably A. iri^ and L. jiojndi have an extremely limited distribution 

 in a few Alpine valleys, and should be included here too, but, curiously 

 enough, one finds them recorded as far south as Central Italy by old 

 writers) ; the other reason is that nearly all the species, which spread 

 in both regions, produce in the Po Basin difterent races from those of 

 Central Europe, though distinctly less so than they are from the races 

 of Peninsular Italy. Anyhow, this question can only be settled when 

 the races of the Northern Italic zone are more thoroughly known. On 

 its south side, as already mentioned, the chain of the .\pennines draws 

 a sharp line between this transitional zone and that of I'vninaular 

 Itah/, w'ith its distinctly southern characteristics. Liguria belongs to 

 the latter, and the great majority of its species and races do not seem 

 to differ in the least, as Avas to be expected, from those of Central 

 and Southern Italy. We will not deal with Liguria in this catalogue 

 because we are not sufficiently acquainted with it. 



The features of the truly Italic races of the Peninsular subzone are 

 obviously due to the marked change of climate, clearly shown by the 

 isothermic winter lines, and of the flora, which strikes one as soon as 

 one has crossed the passes, or in the railway, one comes out of the 

 tunnels of the Apennines, between Piedmont and Liguria, or between 

 Emilia and Tuscany — one enters the region of the olive. Springs are 

 so scarce that all the streams are torrents, and when the water supplied 

 by the winter and spring rains has dried up, the ground becomes baked ; 

 a few storms are in most years all that can be expected from June to 

 September and, in some years and regions, from May till October. As 

 I have pointed out in my paper on " The various modes of eniertjence, 



