THE r-ARNIVOROUS SLUGS OF SOUTH AFRICA. 128 



tlie mantle-border and foot in Paryphanta atramentaria 

 {Sliuttl.), another carnivorous snail. 



Again, the climate has a marked influence on the colour of 

 slugs, moisture being favourable to the development of dark 

 colours, while heat increases the production of red pig- 

 ments. Now in Apera gibbon si rubella both the dark 

 and the red pigments are specially well developed, and this 

 form is at present only known from the coastal region of 

 Natal, Avhich is both moist and warm ; whereas the typical 

 form of A. gibbonsi, as well as the other species inhabiting- 

 the Province, extend further inland. 



Dr. Simi-oth^ has maintained that in Testacella the skin 

 probably plays a more important part in respiration than the 

 lung, and it is suggested that in such slugs as these the chief 

 function of the pigment is to assist in the taking up of oxygen. 

 But it does not seem likely that this is the case in Apera. 

 For in this genus the respiratory tissue of the lung is Avell 

 developed ; while, on the other hand, the structure of the 

 integument and the arrangement of the blood-vessels which 

 it contains do not suggest that the skin plays an important 

 part in respiration. 



On the whole it seems probable that the pigments of these 

 slugs, like those of many other animals, may be looked upon 

 as by-products of metabolism, which are deposited in the skin 

 usually in such a way as to help to render the animal incon- 

 spicuous or to protect it from harmful rays of light, the 

 development of the pigments depending partly on the food, 

 but being also influenced by the climate and surroundings. 

 Yet it must not be forgotten that the coloration of any 

 slug is due not simply to the climate, the food, and the 

 colour of the surroundings, but to the power of reacting to 

 these influences which the animal possesses through inheri- 

 tance. 



' • Nova Acta Acad. Ctesar Leop. -Carol. Germ. Nat. Cur.,' 1891, vol. 

 Ivi, J). 245. 



VOL. 3, PART 2. 10 



