COLORATION AFB'ECTED BY THE EXVIEONMEXT. 67 



the point to which I wish to direct special attention. Deep- 

 sea animals are by no means bleached ; on the contrary, their 

 colours are occasionally even darker than are those of their 

 shallow-water allies ; the brilliancy of the coloration of abyssal 

 animals is one of their most marked characteristics, because it 

 seems at first sight to be opposed to what would have been 

 expected. 



The cave animals are, without exception, " either colourless^ 

 or nearly white, or, as in the case of Arachnida and Insects, 

 much paler than their out-of-door relatives " — " lucicolous " as 

 opposed to " cavernicolous " forms Dr. Packard calls them. 

 The bleaching seems to be more marked in the Myriapods 

 (centipedes, millipedes) than in any other group ; our British 

 centipedes vary in colour from a golden yellow to dark amber- 

 brown, as do those of the United States ; the colour of the 

 cavernicolous species is white, " like a freshly-moulded myria- 

 pod of normal habitat." It should be explained, perhaps, that 

 this change of colour is not due to any bleaching of the 

 integuments, or to their replacement by a white pigment which 

 is so rare in the animal kingdom ; it is simply caused by the 

 white fat body showing through the transparent pignientless 

 " skin." 



The Planarian worms and earthworms living in caves are 

 not entirely bleached, but are distinctly paler in colour than 

 those living beneath the open sky; but, as Dr. Packard remarks, 

 the normal environment of these creatures is not very different. 



There do not seem to be a great number of observations upon 

 the capacity of cave animals for regaining their coloration 

 when exposed to light and ordinary temperatures. Mr. 

 Poulton* has, however, recorded one instance of great interest; 

 a Proteus (a blind, whitish amphibian, living in caves at 

 * " The Colours of Animals," p. 91. 



