So perfect is this transparency that very many of them are rendered
almost entirely invisible when floating in the water, while some, even
when caught and held up in a glass globe, are hardly to be seen. The
skin, nerves, muscles, and other organs are absolutely hyaline and
transparent, but the liver and digestive tract often remain opaque and
of a yellow or brown colour, and exactly resemble when seen in the water
small pieces of floating seaweed." Such marine organisms, however, as
are of larger size, and either occasionally or habitually float on the
surface, are beautifully tinged with blue above, thus harmonising with
the colour of the sea as seen by hovering birds; while they are white
below, and are thus invisible against the wave-foam and clouds as seen
by enemies beneath the surface. Such are the tints of the beautiful
nudibranchiate mollusc, Glaucus atlanticus, and many others.
_General Theories of Animal Colour._
We are now in a position to test the general theories, or, to speak more
correctly, the popular notions, as to the origin of animal coloration,
before proceeding to apply the principle of utility to the explanation
of some among the many extraordinary manifestations of colour in the
animal world.
Pages:
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369