A NATURALIST IN BRAZIL 



a number of such tubular polyps depend from the bladder, which 

 keeps them afloat, and into which a special gland allows gas to 

 enter, inflating it like a balloon. Between the short tubular polyps 

 which absorb nourishment (Fig. 2, S), longer polyps hang down 

 like fine tentacles, whose function is to capture tiny crabs and fishes 

 and convey them to the orifices of the polyps or siphons, whose 

 function it is to absorb and digest. For this purpose they are equipped 

 from top to bottom with batteries of explosive cells or nematocysts 

 which expel extremely fine filaments, and thereby inject a poison 

 into any little fish that swims against them. The fish is immediately 

 paralysed and remains fastened to the tentacle, and this winds 

 itself about its prey, and conveys it, by progressive contraction, to 

 the siphons, which absorb and digest it. These little capillary 

 poison-fangs will penetrate even the human skin; if one touches 

 the Caravella a sharp burning pain is felt. In the case of a large, 

 freshly-taken Caravella the burning may be so acute that inflam- 

 mation and fever will supervene. 



With long drooping tentacles and bladder driven by the wind, 

 the Caravella sails the seas, dredging the waters as with a net that 

 paralyses and kills all living things. Despite the terrible poison- 

 batteries, however, certain little fishes have adapted themselves to 

 this sinister creature, and are found constantly swimming in among 

 the tentacles ; they are protected against many of their enemies by 

 this formidable screen, and at the same time they flourish on the 

 leavings of their living entanglement. 



The polyps of which the Caravella is a living colony are found 

 also as individuals in a profuse variety of forms. On the floor of 

 the sea there are individual polyps which are similar in structure 

 to the nutritive siphons (gastrozoids) of the Caravella, and which 

 live with the closed end of the digestive sac adhering to the sea- 

 bottom; with the mouth-orifice extended upwards, they capture 

 with a circlet of tentacles such creatures as swim within their reach. 

 The wanderer on the beaches of Brazil will not see much of these 

 often resplendently coloured "sea-roses," unless he gazes into the 

 depths of a calm, rocky bay. But there are also natatory forms of 

 hydrozoa. The jelly-fish, sea-nettles, or Medusae are bell-shaped 

 animals which pump their way through the water, rhythmically 

 contracting the rim of the bell. From the circumference of the bell 

 hang tentacles, which, like the snakes of Medusa's head, trail after 

 it writhing and crinkling (Fig. 2). From the centre of the bell the 

 mouth protrudes on a stalk, surrounded by broader pennon-likc 



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