592 
excessive radiation is prevented by fur and 
hair, as in the black skinned Mongolian pony. 
The black skinned animals with little or no 
hair are therefore restricted to a very limited 
thermal range, while those with hair or fur 
protection are healthy in all extremes. 
Some recent observations of horses in the 
Philippines, Japan and Korea have shown that 
slight differences in climate make great differ- 
ences in hair color and it seems to depend 
more largely on air temperature than was 
formerly thought. The detailed data were 
published in a preliminary article in the Sep- 
tember number of the U. S. Cavalry Journal, 
but the point of present interest is the rela- 
tion of pigment to the environmental tempera- 
ture. 
Every kind of protoplasm has a very limited 
thermal range in which it functions best; in 
some cases there is practically no range at all 
for the function is disturbed by even a half 
degree of change. Every kind of protoplasm 
ean live if subjected to higher or lower tem- 
peratures than its optimum even if it ceases 
functioning. But it is to be noted that no 
kind can stand very much rise of tempera- 
ture, though it may be chilled to the absolute 
zero for a short while. The upper thermal 
death point is therefore so near the usual 
range and the malfunctioning due to any rise 
is so great, that each species adopts some safe- 
guard against overheating. In the land mam- 
mals it is always some method of radiation 
or evaporation of perspiration and a dark color 
seems vital for the purpose of radiation in all 
temperatures below body heat. It is amazing 
to see the differences in horse colors in differ- 
ent localities according to temperature in 
Japan, Korea and wherever there has been no 
check to the process by importations for some 
centuries. Where there is heat to reflect at 
any season the color is light or white. 
One of the puzzles of zoology has been to 
account for dense pigmentation where there 
is very little light. If there is complete dark- 
ness, aS in some caves, the color of fishes is apt 
to disappear entirely by selection on the 
ground of economy, the pigment evidently 
being an expensive drain on the resources. As 
SCIENCE 
[N.S. Vou. XXXV. No. 902 
fish are said to have a temperature but little 
above that of the water in which they live, 
there is evidently little or no need for them to 
have safeguards against overheating or chill- 
ing in a medium, never hot enough to be in- 
jurious nor below 40° F. as a rule. Hence 
coloration of fishes has been invariably inter- 
preted as for concealment, and the facts cer- 
tainly do point to that reason. 
In the deep sea, on the other hand, we have 
vastly different conditions. The only light is 
a phosphorescence which is usually so faint as 
to require very large eyes, yet some investi- 
gators assure us that it can be so intense as 
to demand dense pigmentation for conceal- 
ment. This may account for the fact that the 
pigment is often spread all over the body, as 
would be necessary if the light comes from all 
directions and not always from above, as in 
the fishes of the upper layers. Yet there are 
curious exceptions, as though some deep sea 
places were as dark as caves, for some species 
have little or no pigment and some have no 
eyes; but as far as known, the relation between 
these facts, if there is any relation at all, has 
never been explained or proved. 
With regard to deep sea temperatures we 
are assured that generally they are very low, 
specimens being too cold to handle. Salt 
water at such pressures can be much below 
32° F. without freezing, and it is often found 
at a degree which prevents all activity of fisk 
in surface waters. They “hibernate” in such 
chilly surroundings. There must then be a 
different law as to the relation of the body 
temperature of deep sea fish to the water sur- 
rounding them. AI] the mammals of the sea 
are densely pigmented and generally all over. 
They are never subjected to high temperatures 
nor to anything lower than 32°, and have no 
need for protection from extremes. The pig- 
ment then must be for light protection. They 
all prevent undue heat loss by the thick layer 
of insulating fat, so the radiation of heat by 
the black color can do no more harm than in 
the case of black cattle which are found in 
mild temperate climates. Black pigments can 
not be for the purpose of absorbing heat from 
the sun’s rays, for all such animals avoid the 
