[11] THE BOTTOM OF THE GULF STREAM. 1055 



Other important facts, bearing directly, not only on tlie existence, but 

 on the quality, of the light, are those connected with the coloration of 

 the deep-sea species. In general it may be said that a large proportion 

 of the deep-sea animals are highly colored, and that their colors are cer- 

 tainly protective. Certain species, belonging to different groups, have 

 pale colors or are translucent, while many agree in color with the mud 

 and ooze of the bottom, but some, especially among the fishes, are very 

 dark or even almost black. Most of these are probably instances of 

 adaptations for protection from enemies or concealment from prey. But 

 more striking instances are to be found among the numerous brightly 

 colored species belonging to the Echinoderms, decapod Crustacea, 

 Cephalopods, Annelids, and Anthozoa. In all these groups species 

 occur which are as highly colored as their shallow-water allies, or even 

 more so. But it is remarkable that in the deep-sea animals the bright 

 colors are almost always shades of orange and orange-red, occasionally 

 purple, purplish-red, and brownish-red. Clear yellow, and all shades 

 of green and blue colors are rarely, if ever, met with. These facts indi- 

 cate that the deep sea is illuminated only by the sea-green sunlight that 

 has passed through a vast stratnm of water, and therefore lost all the 

 red and orange rays by absorption. The transmitted rays of light 

 could not be reflected by the animals referred to, and therefore they 

 would be rendered invisible. Their bright colors can only become visi- 

 ble when they are brought up into the white sunlight. These bright 

 colors are, therefore, just as much protective as the dull and black colors 

 of other species. 



The deep-sea star-fishes are nearly all orange, orange-red, or scarlet, 

 even down to 3,000 fathoms; the larger Ophiurans are generally orange, 

 orange-yellow, or yellowish white, the burrowing forms being usually 

 whitish or mud-colored, while the numerous species that live clinging to 

 the branches of gorgonians and the stems of Pennatulacea are generally 

 orange, scarlet, or red, like the corals to which they cling. Among 

 such species are Astrochele Lymani, abundant on the bushy orange gor- 

 gonian coral, Acanella Normani, often in company with several other 

 orange Ophiurans, belonging to Ophiacantha, etc. Astronyx Loveni and 

 other species are common on Pennatulacea, and agree very perfectly in 

 color with them. These and numerous others that might be named are 

 instances of the special adaptations of colors and habits of commensals 

 for the benefit of one or both. Many of the large and very abundant 

 Actinse or sea-anemones are bright orange, red, scarlet, or rosy in their 

 colors, and are often elegantly varied and striped, quite as brilliantly 

 as the shallow water forms, and the same is true of the large and ele- 

 gant cup-corals, FlaMlum. Goodei, F. angulare, and Caryophyllia com- 

 munis, all of which are strictly deep-sea species and have bright orange 

 and red animals when living. The gorgonian corals, of many species, 

 and the numerous sea-pens and sea-feathers (Pennatulacea), which are 

 large and abundant in the deep sea, are nearly all bright colored, when 



