IgO THE ZOOLOGIST. 



species, which have followed the ahove-mentioned line of immigra- 

 tion, are found. There is also, thirdly, a considerahle difference 

 in size and colouring and, what is more important, in the method 

 of distribution between the L. muralis of Baden and that of the 

 Bavarian Palatinate, which could hardly be so marked, if both 

 had penetrated into Germany from the same source. 



It may therefore be asked whether this species has not, 

 following the course of the Danube, descended further westwards 

 from the central plateau of the Black Forest along the many 

 small rivers on whose banks it now is found. Certainly this would 

 pre- suppose its former existence in localities where it no longer 

 occurs, and hence possibly a change of climate within a geologically 

 recent period in these comparatively bleak regions. Still this 

 hypothesis appears the less improbable as other species have 

 unquestionably immigrated by this line, and also in view of the 

 fact that L. muralis, like L. viridis, occurs on the Danube east of 

 the Swabian and Bavarian table -lands.* If the immigration 

 along the Danube therefore has not taken place at a very early 

 period, we can sufficiently account for its present singularly 

 restricted distribution by assuming a diminished ratio of increase 

 in this less congenial climate. Besides, the " stationary distribu- 

 tion" characteristic of the Lacertidce, will prevent any further 

 emigration until the district occupied has become over-populated. 

 And there are indications of such local over-population. Thus 

 it may be observed that from Gerusbach in the Murg-valley 

 (where this species is very abundant) it is spreading across the 

 narrow watershed into the valley of the Oos, in which Baden- 

 Baden lies; but the transmigration is as yet incomplete, for it 

 appears to occur only on the Gerusbach side of the Oos valley. 



As regards the distribution of this species in the Grand 

 Duchy, my experience is confirmatory of the account above 

 referred to. It is found on several of the old castles in the 



* This point need not have been reached exclusively from Lower Austria, 

 but also from N. Italy. For L. muralis has been observed to cross the 

 Brenner-pass, and may accordingly have come via the valley of the Inn 

 (H. Krauss, 'Verhandl. Zool. Bot. Ges. Vienna,' 1873), whilst another 

 author reports its occurrence in the higher course of the same river,— at 

 Pfunds and Landeck, — which would imply an emigration from the south, 

 parallel to that over the Brenner, by way of the Vintschgau. (I may mention 

 that I never observed it at either of these localities.) 



