Pyrosojiatid^e. MOLLUSCA. PyfiOsoma gigasteum. 



385 



Family IV.— PYROSOMATIDiE. 



The Pyronoraas are compound animals; but instead 

 of being fixed, they are free and floating on the surface 

 of the ocean. 



Genus Pyrosoma. — This genus is the only one at 

 present belonging to the family. The common body 

 of this peculiar genus of Tunicaries is semicartilaginous 

 and noncontractile — the individuals of which the aggre- 

 gate mass is composed forming a hollow cyliuder from 

 two to fourteen inches long, a half-inch to three inches in 

 circumference, and open at one extremity only. These 

 individuals are grouped in whirls each having two ori- 

 fices, one at each end. They are united at the circum- 

 ference of the middle portion by the fusion of the tests 

 to one another into rings more or less regular, and 

 varying in number according to the species, so that the 

 whole forms the cylinder above described. — [Rupert 

 Jones.) Their orifices are so arranged that the inhalant 

 openings are external, the inhalant inside the tube ; and 

 the result of so many little currents discharged into the 

 cavity is to produce one general outfiow, which impels 

 the floating cylinder with its closed end foremost. — 

 ( Woodtoard.) The individuals composing this curious 

 floating cylinder amount, in the adult Pyrosoma, to 

 several thousands, forming, in fact, a numerous colony, 

 each little mollusk in its own cell, distinct, yet insepar- 

 ably connected with its fellows. The Pyrosomas are 

 gregarious animals, and often occur in great numbers. 

 They are found in the warmer parts of the great ocean, 

 and at times they are so abundant in the Mediterranean 

 that they have been found to clog the nets of the fisher 

 men. Their delicate and transparent forms, and their 

 elegant tints of colour, render them beautiful objects as 

 seen floating during the day on the tranquil bosom of 

 the sea; but their splendid phosphorescent property, 

 the brilliant light which they give out at night as they 

 glide past the vessel, have made them still more the 

 objects of admiration to voyagers and naturalists. The 

 descriptions given by many such are exceedingly inter- 

 esting. The celebrated Humboldt, describing his 

 having seen the P atlaniicum on his voyage to South 

 America, says that it gave a light of a foot and a half 

 in diameter while swimming beneath the surface. 

 " Only imagine," he says, " the superb spectacle which 

 we enjoyed when in the evening, from six to eleven 

 o'clock, a continuous band of those living globes of fire 

 passed near our vessel. With the light which they 

 diffused we could distinguish at a depth of fifteen feet 

 the individuals o(T/iynmi3, Pelamys, and Sardon, which 

 have followed us these several weeks, notwithstanding 

 the great celerity with which we have sailed." Dr. G. 

 Bennett, in his interesting " Wanderings," tells us that 

 the ves.sel in which he was, continued, while proceeding 

 at a rapid rate, during the whole night to pass through 

 distinct but extensive fields of Pyrosomas, floating, and 

 glowing as they floated, on all sides. Enveloped in a 

 flame of bright phosphorescent light, he adds, and 

 gleaming with a greenish lustre, these creatures seen 

 at night, in vast shoals upwards of a mile in breadth, 

 and stretching out till lost iu the disUuice, present a 

 spectacle the glory of which may be easily imagined. 

 The vessel, as it cleaves the gleaming mass, throws up 

 Vol. U. 



strong flashes of light as if ploughing through liquid fire, 

 which illuminates the hull, the sails, and the ropes with 

 a strange unearthly radiance. M. Peron, the French 

 naturalist, was, perhaps, the first who recorded this 

 phosphorescent quality of the Pyrosomas. It was in a 

 squall out at sea that his attention was called to the 

 phenomenon. " Suddenly," he says, " we discovered at 

 some distance a great phosphorescent band stretched 

 across the waves, and occupying an immense tract in 

 advance of the ship. Heightened by the surrounding 



Pyrosoma gi;;aiitcuni. 



circumstances, theefibct of this spectacle was romantic, 

 imposing, sublime, rivetting the attention of aU on 

 board Soon we reached the illuminated tract, and 

 perceived the prodigious brightness was certaiidy and 

 only attributable to the presence of an innumerable 

 multitude of largish animals floating with the waves. 

 From their swimming at diflerent depths they took, 

 appaventlv, diflerent forms; those at the greatest deplh 



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