UiG 



GENUS ARION. 



Variation. — In Ar/nii tlie pigmentation lias resolved itself into two 

 chief colonrs : one dusky or black producing the markings, and the other 

 various shades of red, both of which in the larger and niijre variable 

 species by their development or degeneration ([uickly show, especially 

 during the growth jieriod, the effects of varied environment, mirroring 

 back in the' slug's body the effect of climate, etc. Cold and moisture 

 being favourable to the ile\'elopment of the ilusky pigment ami warmtli and 

 dryness to the red. 



'I'lie darker varieties are f lund most numerously in the nortliei'u regions 

 and ill moiiutaiiinus districts, ;i.nd this melaiiii- tendenc^r is correlated with 

 •■i. stiiiiter and coarser condition of the skin, .and by a bidder tuberculation, 

 whili^ the lirighter c(doured firms are pi'obalily the outcome of a dry and 

 warm environment, and though these factors .'ire not the only ones that 

 foster a brillianc)' of colouring or the reverse, yet they uudoubtedl}' have a 

 very marked influence thereon. 



The largest and most advanced species are those most actively engaged 

 in the elaboration of new firms, but it is amongst the smaller and more 

 primitive species that con\'ergence is most evident, ami which display most 

 strikingly their commmi ixdationship to an ancestral form. 



Geographical Distribution. — The .1 rions are European in origin and 

 distribution, aHertiiig more [larticularly the western area; members of 

 the group liave, lii.iwi'\-cr, spread into Siberia, North Africa, Azores, 

 Madeira, etc, and thmu^ii the agency of commerce have secured a footing 

 ill North America and ntlier places. 



It has, however, been erroneously supposed by Bourguignat and other 

 .■dile scientists that. Arion, as well as other genera, originated on the 

 t'entral Asian plateau, and spread into Europe by way of the great 

 northern coniferinis belt, or along the mountain chains of Central Europe, 

 wliiii' other modern authors believe the Iberian peninsula or the lost 

 Atlantis to be the true birthi)lace of the group. 



I'M. ISI.--A M,-ikuolouir,nl I.nlinr.Uni-y 

 Ml-. W. K. Collir,-> :iL the ll„i vr, ^ii y, I'.ii nn,i,i;l,.-,m 



