COLORATION AFFECTED P.Y THE ENVIRONMENT. 59 



night-heron (Ni/cticoi-a.r pauper} is, according to Mr. Salvin's 

 diagnosis of the species, " similis N. riolaceus sed multo 

 obscurior.'' Larus fuliginosus is a gull which might be con- 

 founded with the Chilian L. modestus, were it not for its black 

 hood. 



Coront'lla pliocarum, of Robben Island, is nearly allied to the 

 South African (\ cam, a variable snake, but generally paler 

 in colour. 



Further Examples of the Effects of Temperature and Moisture. 



The English fritillary (Aryynnis papltia} is known to occur 

 as a dark variety, which has been called " valezina " ; this 

 variety appears to be almost confined to wooded countries, 

 and the question is whether the moisture of such localities is 

 responsible for the darker coloration. 



The dark coloration of lizards in oceanic islands has been 

 already mentioned; such situations are, of course, pre-eminently 

 moist. 



There are other facts which show that moisture, rather than 

 temperature, is the cause of a darkening. Dr. Eimer has 

 commented upon the prevalence of a dark colour in the slug 

 (Arion empiriconuii) during wet summers in the neighbour- 

 hood of Tubingen; but the same naturalist found dark-coloured 

 slugs on the summits of hills where there was but little 

 moisture; and there are other cases of darker-coloured varieties 

 of animals found in elevated localities. Dr. Eimer considers 

 that in all probability elevation, as well as moisture, is 

 effective in producing such colour changes. 



There is no reason whatever against accepting this sugges- 

 tion ; seeing that there are constitutional differences among 

 individuals of one species, it may easily be believed that thep 

 are such differences between different species and gej^J^ s 



> ~ 



00 - 



