16 THE ATLANTIC. [chap. i. 



tent, and such expanses are probably more frequent nearer the 

 centre of its area of distribution. 



They consist of a single layer of feathery bunches of the 

 weed {jSm^gassum bacciferum), not matted, but floating nearl}^ 

 free of one another, only sufliciently entangled for the mass to 

 keep together. Each tuft has a central brown thread-like 

 branching stem studded with round air-vesicles on short stalks, 

 most of tliose near the centre dead, and coated with a beauti- 

 ful netted white polyzoon. After a time vesicles so incrusted 

 break off, and where there is much gulf -weed the sea is studded 

 with these little separate white balls. A short way from the 

 centre, toward the ends of the branches, the serrated willow-like 

 leaves of the plant begin ; at lirst brown and rigid, but becom- 

 ing farther on in the branch paler, more delicate, and more 

 active in their vitality. The young fresh leaves and air-vesicles 

 are usually ornamented with the stalked vases of a Campanu- 

 laria. The general color of the mass of weed is thus olive in 

 all its shades, but the golden olive of the young and growing- 

 branches greatly predominates. This color is, however, greatly 

 broken up by the delicate branching of the weed, blotched with 

 the vivid white of the incrusting polyzoon, and riddled by 

 reflections from the bright -blue water gleaming through the 

 spaces in tlie net-work. The general efl^ect of a number of such 

 fields and patches of weed, in abrupt and yet most harmonious 

 contrast with the lanes of intense indigo which separate them, 

 is very pleasing. 



These floating islands have inhabitants peculiar to them, and 

 I know of no more perfect example of protective resemblance 

 than that which is shown in the gulf -weed fauna. Animals 

 drifting about on the surface of the sea, with such scanty cover 

 as the single broken layer of the sea -weed, must be exposed 

 to exceptional danger from the sharp-eyed sea-birds hovering 

 above them, and from the hungry fishes searching for prey be- 

 neath ; but one and all of these creatures imitate in such an ex- 



