PROTECTIVE RESEMBLANCES, AND MIMICRY 207 
color and general external appearance the surface of the 
object on which they rest (Figs. 127 and 128). 
109. Special protective resemblance.—Far more striking 
are those cases of protective resemblance in which the ani- 
mal resembles in color and shape, sometimes in extraor- 
dinary detail, some particular object or part of its usual 
environment. Certain parts of the Atlantic Ocean are 
covered with great patches of sea-weed called the gulf-weed 
(Sargassum), and many kinds of animals—fishes and other 
creatures—live upon and among the alge. No one can 
fail to note the extraordinary color resemblances which exist 
between those animals and the weed itself. The gulf-weed 
is of an olive-yellow color, and the crabs and shrimps, a cer- 
tain flat-worm, a certain mollusk, and a little fish, all of 
which live among the Sargassum, are exactly of the same 
shade of yellow as the weed, and have small white markings 
on their bodies which are characteristic also of the Sargas- 
sum. The mouse-fish or Sargassum fish and the little sea- 
horses, often attached to the gulf. weed, show the same traits 
of coloration (Fig. 129). In the black rocks about Tahiti ~ 
is found the black nokee or lava-fish (Zmmydrichthys vul- 
canus) (Fig. 66), which corresponds perfectly in color and 
form to a piece of lava. This fish is also noteworthy for 
having envenomed spines in the fin on its back. The 
slender grass-green caterpillars of many moths and butter- 
flies resemble very closely the thin grass-blades among 
which they live. The larve of the geometrid moths, called 
inch-worms or span-worms, are twig-like in appearance, 
and have the habit, when disturbed, of standing out stiffly 
from the twig or branch upon which they rest, so as to re- 
semble in position as well as in color and markings a short 
or a broken twig. One of the most striking resemblances 
of this sort is shown by the large geometrid larva illus- 
trated in Fig. 130, which was found near Ithaca, New York, 
‘The body of this caterpillar has a few small, irregular spots 
or humps, resembling very exactly the scars left by fallen, 
