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 algae. 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 f 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 (Emmydrichthys 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 larvae 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 



