ASSIMILATIVE COLOURATION. 455 
Ohio or Schuylkill; those of the reddish-coloured waters of the 
bayous of the Louisiana swamps look as if covered with a coppery 
tarnish; and, lastly, those met with in streams that glide beneath 
cedars or other firs have a pale and sallow complexion.”’* A no 
less authority than Dr. Gunther states: ‘‘ Trout with intense 
ocellated spots are generally found in clear rapid rivers, and in 
small open alpine pools; in the large lakes with pebbly bottom 
the fish are bright silvery, and the ocellated spots are mixed with 
or replaced by X-shaped black spots; in pools or parts of lakes 
with muddy or peaty bottom the Trout are of a darker colour 
generally, and when enclosed in caves or holes they may assume 
an, almost uniform blackish colouration.” + ‘‘ Minnows have the 
power common to most fishes of rapidly assimilating to the 
varying colour of the stream. They change from brown to gold, 
from goid to brown.’ { The Paradise-fish (Polyacanthus sp.), a 
pet kept in confinement throughout China, has a colour in dark 
or muddy waters of a ‘‘dull uniform brown; and it is only when 
living in clear water, exposed to the sunlight, that the golden hue 
and red transverse bands make their appearance.” ‘‘Cod from 
the British seas and German Ocean are usually greenish or 
brownish olive in colour, with a number of yellowish or brown 
spots; but more to the north darker, and often uniformly coloured 
Specimens are more common; while in the race from Greenland, 
Scandinavia, and northern Norway, there is frequently a large 
irregular black patch on each side of the body.” § In the South 
Atlantic Mr. Cunningham secured by the aid of the towing-net a 
bright blue Isopodous crustacean (Idotea annulata), and states 
that, according to Spence Bate, “‘the blue colour appears to be a 
peculiarity of pelagic species.”’|| 
Entomologists have long noticed the effects of assimilative 
colouration, even in our own country. Mr. Dale, of Glanvilles 
Wootton, has truly remarked: ‘‘ Where do we find whitish or 
brilliant-coloured species of Lepidoptera, such as Melanargia 
galatea, Lycena corydon, L. adonis, Hubolia bipunctaria, Mela- 
* Audubon and his Journals,’ vol. ii. p. 519. 
+ ‘Introd. Study Fishes,’ p. 632. 
t Watson, ‘Sketches of Brit. Sport. Fishes,’ p. 77. 
§ Lydekker, ‘Roy. Nat. Hist.,’ vol. v. pp. 412, 483. 
|| ‘ Notes Nat. Hist. Strait of Magellan,’ p..42. 
212 
