55 



SOME REMARKS ON THE COLOUR CHANGES 

 IN ARION INTERMEDIUS, Normand. 



By W. A. GAIN, 

 foint Editor, Moltitscan Section, "British Naturalist" ; Tnxford, Newark. 



It appears to me that we shall be obliged to greatly reduce the 

 number of varieties generally accorded to our British Slugs, for 

 many of the forms usually considered distinct are merely stages in 

 the growth of a variety or species ; probably to write a full history of 

 any species it will be found requisite, not only to describe a number 

 of varieties, but under each variety to group the forms through which 

 it successively passes. Arion empiricomm, Fer., as is well known, 

 darkens with age, in many cases passing through stages of colouring 

 quite distinct from that which it finally assumes. Of this slug 

 I hope to say more at a future time, as I have a number at present 

 under observation, and am taking notes of the colour changes. 



In A. intermedins the general change of colour appears to be 

 from dark to light. I have known this slug in its young state either 

 as dark green or yellow. On April 9th, 1892, I obtained a number 

 of the green-coloured variety, and the following notes record the 

 various changes : — 



On May 24th they had " slightly grown ; greenish-yellow in colour, 

 with more or less distinct slaty lines." 



June 5th. — " Larger, and have lost the green colour, now yellow, 

 more or less bright, with well-developed lines, one specimen 

 with a dusky line down the centre of the back." 



June 17th. — "All four living, three full-grown. All very pale 

 yellow, almost white, uniform except sole and slime gland, which are 

 rather deeper. No lines on the sides of the body or around the 

 mantle." 



June 29th. — "One appeared above the soil after watering," — they 

 frequently penetrate into loose soil — "light yellow and bandless." 

 After a second watering another specimen came to the surface, "light 

 yellow, almost straw-colour, with a very light touch of grey on the 

 centre and edge of the mantle, slime gland rather darker yellow, 

 almost unicolour." 



July 8th.—" Retired below the surface." 



July. — " Very pale yellow, almost white, colour nearly uniform, 

 except slime gland and sole, which are rather deeper, no lines on 

 the sides of body or around the mantle." 



