BRITISH SLUGS 



1081 



Arions as sulky, and distinctly trying as 

 camera subjects. When touched they 

 contract into hemispherical balls, remain- 

 ing so for a considerable time, keeping up 

 a slow rocking mo\'ement like a boat in 

 water at ebb-tide. Some suppose that 

 this action is intended to intimidate the 

 enemy ; from the human standpoint it 

 is eminently ridiculous and exasperating 

 when you want to get a picture of Arion 

 extended. The slug measures from three 

 to live inches ; the colouring is variable, 

 the black and the red the two main 

 t\'pes. They can be regarded as primary or 

 climatic distinctions of colour — the black 

 with cold and wet locahties ; the red with 

 warm and dry ones. It has been noted 

 that the pigment cells in the skin of red 

 varieties are affected by a wet season, 

 when the number of black slugs is in- 

 creased. The -\merican t\'pes show links 

 with this group which relate our Arions 

 with a tribe not originally shell-less, but 

 possessed of spirally formed shells. 



In addition to fifteen varieties of clearly 

 differing colour scheme, there are other 

 accepted sub-varieties. Arion ater, black, 

 have a sub- variety A. aterimma, black, 



with the " foot-sole " dark also, a more 

 uncommon slug. The specimen for 

 illustration was one of these, the " foot- 

 sole " being a dark slaty blue, from York 

 district. Castanca, dark brown, with burnt 

 sienna "foot-fringe"; Pliimhea, pur])lish 

 grey, with yellow " fringe " ; Rufa, burnt 

 sienna, with orange " fringe " ; Snccinea, 

 bright yellow, with orange " fringe " ; 

 Alba, white, with yellow " fringe " ; 

 Hiherna ; Bocagei ; Alhalatoralis, black 

 and white, with orange " fringe " ; Bi- 

 color ; Reticulata, yellow ochre, with 

 redder " fringe " and broad brown patch 

 on " shield " and back, tentacles black ; 

 Fasciata, type f(jrm Briinneo-fasciata, warm 

 browTi, dark on sides, paler below, " fringe " 

 yellowish ; Marginella ; and Macidata. 



The eggs are laid in great numbers in 

 all seasons of the j'ear, sometimes as early 

 as January, under stones, wood and dead 

 \'egetation ; twenty to fifty in batches 

 that hatch out. according to temperature, 

 in from thirty to fifty days. Four types 

 of Arion stand apart from ater in certain 

 important characteristics : 



I. A. sithjuscns is smaller, measuring 

 from two to three inches, and does not 



EGGS OF SLUG hN TUKF. 



137 



