94 
VARIATION IN COLOUR. 
which the colouring has been arrived at. A modified form of Ilelir 
virgatd var. rufiila, with tlio bands present as in the t)"pical form, is 
an interesting illustration of this phase of colouring (see pi. ii., fig. 3). 
IMelanism (/xo\ur, black) is the opposite condition to albinism, and 
is a consequence of the excessive action or hypertrophy of the colour 
glands diffusing the colouring matter of the bands or other markings 
over the snrfiice of the shell, and when this diffused pigment is black, 
or approximately black in colour, the phenomenon is termed melanism. 
'SI iss F. i\I. Ilele has observed that certain foods have an inflnence 
upon the colouring of growing Ile/I.r (ispersa, as those specimens fed 
upon lettuce leaves always ac(piired a darker colour, or the colouring 
matter became more overspread than was usually the case, and Mr. 
Standen has also recorded that the sinistra! Helix afipersa which he 
fed to maturity upon “dainty food” lost its mottleil markings and 
became almost uniformly black. The coalition of the black bands in 
Helix nemnr(iH!f, etc., is a well known and common example of this 
phenomenon ; a still more striking illustration being furnished by 
the Helix circjdfd var. nigvet^cens (see jil. ii., fig. 2), which has been 
observed by i\Ir. Ashford to be a very local form in tbe Isle of Wight 
and to live chiefly upon Cdrclniis tenuifulius, but Mr. II. B. Ilewetson, 
of Leeds, has foumi some very characteristic specimens of this variet}" 
upon the Ragwort (Sedecio j((enlurd), on the sand-hills at Kilnsea, 
near Spnrn, Yorkshire. 
Eryturism ( epvHpiH , red) and Erythrochroism are the terms ex- 
pressing the development of the red pigment (see pi. ii., figs. G, 7, 9), 
and would seem to be a biological exi)ression of a warm climate or 
season, as we meet with this red form in Helix iiemornlis and Helix 
l/(irteiisis much more i)lentifully and more richly coloured in the 
southern counties of England than in the northern parts of the 
country. This erythrous condition or colouring as existing in the 
shell of Helix hortensi^ has been considered by Herr Weiidand, 
under certain circumstances, to be protective in character, as for 
instance, when the animal resides amongst fallen beech leaves, and he 
has therefore distinguished and named this form the variety 
owing to finding the shells in snch situations. Xanthous variation 
(j)l. ii., fig. 1 l)when not pure would seem to be very closely associated 
or connected with erythrism, and is often developed during gvowth as 
a modification of the red colouring existing in early life or rice re?'sd. 
