122 HUGH WATSOX, 



di'owned by Mi*. Burnup, tlie red pig^ment came out of the 

 skin when the animal was dead, and coloured the water in 

 which the slug was immersed. Notwithstanding the dai-k 

 grey mottling of this foimi, the living animal is of a reddish 

 colour, changing to orange below, as the unstable colouring 

 matter is sufficiently abundant to mask the darker pigment 

 underneath. 



The coloration of a typical specimen of A per a gibbon si 

 increases its i-esemblance to the rhizome of a fern, and the 

 chestnut-ln'own colour of A. burnupi may help to render 

 the slug inconspicuous among dead leaves. Even the reddish 

 colour of A. gibbonsi rubella may serve to conceal the 

 animal, although the bright pigment of the red variety of Arion 

 ater is supposed to act as a wai-ning colour. Mr. Burnup 

 found a specimen of this Apera in the bush at Durban, and 

 he noticed that a few of the dead leaves^ under which the 

 slug was found were of a dark brownish-red colour, strongly 

 veined, and curled up into rolls, and these were so very like the 

 slug that it might easily have been mistaken for one of them. 



On the other hand, it seems possible that the vmstable red 

 and orange pigments found in Apera and other slugs which 

 are often carnivorous, as well as the similar bright colours so 

 characteristic of most of the snails belonging to the Strep- 

 taxi das, may be partly due to their animal food. It is known 

 that this is the case with the red pigment found in the 

 flamingos, the scai'let ibis, and the roseate spoonbill ; for the 

 colour tends to disappear when the birds are deprived of their 

 natural food, which consists chiefly of mollusks and other 

 invertebrates. M. F. Woodward- has described the rich 

 orange colour of the edge of the mantle in specimens of 

 Natalina caff ra which were fed on snails and beefsteak, 

 and Miss Davies^ mentions the brilliant orange-red colour of 



' Dr. J. Medley Wood, Director of the Natal Herbarium, has kindly 

 examined one of these leaves, and thinks that it prol)a]3ly lielongs to 

 Combretum krausii. 



- 'Proc. Mai. Soc.,' 1895, vol. i. p. 271. 



3 'Proc. Roy. Soc. Yietoria.' ^9V.^. vol. xxi. p. 222. 



