FLOUNDER-FISHES. 
367 
Both Pouchet and Agassiz (1. c.) succeeded best in 
their experiments on specimens of Bothns which were 
shifted from vessels and bottoms of different colours 
and into different lights, always with the result that on 
a dark bottom and in dark environments the fish turns 
dark, while it assumes a lighter tint when the circum- 
stances are reversed. In this manner it conceals itself 
in its free state, either to lie in ambush for some victim 
or to escape the notice of some foe. But Pouchet, 
whose subjects were Turbots of different sizes, varying 
in length between 6 and 25 cm., found that they lost 
this power of changing colour when he blinded them, 
and also forgot to cover themselves with sand when 
placed on a. sandy bottom, an end which they other- 
wise attain quite skilfully by a few sharp strokes with 
the hind part of the body. It was thus evident that 
sight was a necessary adjunct of the changes of colour. 
The visual sensations pass from the eyes to the brain, 
where they are exchanged for nervous vibrations that 
start the expansion or contraction of the chromato- 
phores; and these nervous vibrations, according to 
Pouchet, are conveyed partly along the Trifacial nerve 
(the fifth pair of nerves in the head), partly by the 
great sympathetic chain of ganglia, to the spinal nerves. 
The spinal cord itself, according to Pouchet’s investi- 
gations, does not play the least part in the transmission 
of these vibrations; but the sympathetic nervous chain 
which lies beneath the vertebrae on each side, and is 
connected with the cranial nerves, especially with the 
Trifacial nerve, sends out branches to each pair of the 
spinal nerves. If these nerves are destroyed in that 
part of their course that contains elements of the sym- 
pathetic nervous system, they also lose the power of 
transmitting any influence to the chromatophores. This 
connexion between the action of the brain and that of 
the sympathetic nervous system on the chromatophores 
in the skin, may well serve as an explanation of the 
blending — in many cases quite incomprehensible — of 
voluntary and involuntary changes in the colour of the 
skin under the influence of phenomena of light or sen- 
sual impressions, a circumstance which may often be 
observed even in the higher animals. The development 
of the spawning-dress seems also to lie due chiefly to 
the influence exercised by the sympathetic nervous sy- 
stem at the time for the higher development of the 
generative organs and their maturation. 
" Pouchet, who proposes to reserve the name of chromatopl 
example — calls these more protoplasmatic cells chromoblasts. 
Besides the iridocytes of Pouchet — pigmental bodies 
or cells containing powerfully refractive, microscopical 
disks arranged in parallel lines or heaped like the coins 
in a roll, to the presence of which bodies the gray 
colour of the skin of the Flounders is due — we here 
find chromatophores" of black, yellow and red. The 
black chromatophores, which are always more or less 
ramified when they expand, but may contract into a, 
tiny dot, lie nearest the surface; and the position of 
the yellow and red varies considerably in the different 
species. The varying expansion or contraction of these 
cells, is adapted to the colours of the surroundings of 
the fish, and produces that arrangement of colours on 
the eye side of the Flounders which sometimes renders 
them so difficult to discover. 
Thus, the nervous system and, in particular, the 
sense of sight are the determinant factors in the changes 
of colour; and Pouchet has also shown that habit exer- 
cises no small influence on this faculty. Out of a num- 
ber of Turbots that were kept alive in a well, he se- 
lected the palest. He then put it in a vessel with a 
brown bottom, and five days elapsed before the fish 
could adapt its colour to that of the bottom. He now 
moved it to a, light sandy bottom, and in two days 
the fish had regained its former light colour. Again 
he moved it to a brown bottom, and now only two 
hours produced the same effect as it had taken five 
days to gain before. “The faculty of changing colour,” 
says Pouchet, “is thus influenced by habit, and this 
too, soon enough, for the Turbot in question had lived 
at most only three months on the light bottom where 
Ave found it. From an anatomical point of vieAv it is 
very difficult to explain this habit. Perhaps the nerves 
that start the contraction or expansion of the chromatic 
cells, are in some Avay paralysed by Avant of exercise, 
and require some time to recover from this paralysis. 
Or have the chromatic cells lost too much of their con- 
tractile matter? Or must AA-e look for the reason of 
their immobility outside them: perhaps in the surround- 
ing tissues, the resistance of Avhich prevents the ex- 
pansion of the cells? All these are questions to Avhich 
no ansAver can be given at present. But Ave can easily 
realise that the fact that habit thus gains influence so 
quickly, is of some zoological importance. As it can 
be shoAvn that the faculty of changing colour may be 
restricted in so short a time, Ave must also ackrioAvledge 
lores for the more developed chromatic cells — in the Cephalopoda for 
