ASSIMILATIVE COLOURATION. 398 
Porchinsky, one of a scientific party engaged in exploring the 
Caucasus, also witnessed a nearly complete phenomenon of 
assimilative colouration. The southern limit of the region ex- 
plored was the steppe of EHrivan, a plain covered with sand, with 
some patches of variously coloured clays appearing in the low 
hills. A remarkable feature of the animal inhabitants of the 
steppe, insects and reptiles, and especially of the Lizards, is the 
most perfect agreement of their colouration with that of the 
steppe. The same thing was also observed in the steppe of Eliza- 
bethpoi.* This is a similar observation to that made by Canon 
Tristram in North Africa, and induces the same comment. Dr. A. 
Leith Adams remarks :—‘‘ The colour of the plumage of many 
desert-loving birds, like the denizens of arctic regions, assimilates 
to that of surrounding objects, and, moreover, as has been truly 
said, we also find the bleaching influence of the desert, and the 
dry and cloudless climate imparting their hues to the Egyptian 
monuments. So much is the latter the case that the eye fails at 
first to receive an impression of their immense antiquity, owing 
to the absence of the grey colouring and weather stains which 
give so venerable an aspect to those of Northern Europe. There 
is thus a stamp imprinted on all the animate and inanimate 
objects, in accordance with their haunts, as, for example, the 
desert Chats and other birds are much paler in colouring than 
those which frequent the cultivated districts on the river’s banks.’’t 
If this appears to be evident on the surface of the earth, the 
same phenomena seem to exist in the abyssal depths of the 
ocean. From recent deep-sea researches we know that the floor 
of the ocean is probably a vast undulating plain of mud; and, to 
quote both Sir John Murray and Mr. Hickson, of all the deep- 
sea deposits, the so-called ‘‘red mud” has by far the widest 
distribution. According to the testimony of the late Prof. 
Wyville Thomson and his colleagues in the ‘ Challenger’ Ex- 
pedition, this red clay is the residuum left after the calcareous 
matter of the Globigerine ooze has been dissolved away; and 
Sir John Murray is of opinion that “ probably the majority of 
deep-sea species live by eating the surface-layers of the niud, 
clay, or ooze at the bottom, and by catching or picking up the 
* Commun. to St. Petersb. Entomol. Soc.; see ‘ Nature,’ vol. xv. p. 16. 
+ ‘Naturalist in the Nile Valley and Malta,’ pp. 50, 51. 
Zool. 4th ser. vol. II., September, 1898. 2D 
