1192 



TUNICATA. 



Family PYROSOMID^E. Synonyms : Lucies 

 composees, Savigny ; Tuniciers reunis, pars, 

 Lamarck ; " les agreges^ pars, Cuvier ; Sal- 

 piens agreges, Blainville; Lucidce, MacLeay; 

 Pyrosomiens, Milne-Edwards and Van Bene- 

 den. The Pyrosomians are represented by three 

 or four species of the single genus Pyrosoma. 



They inhabit the Mediterranean and the 

 warmer parts of the ocean ; in the former at 

 times their abundance is a source of dread to 

 the fishermen, sometimes even completely 

 clogging their nets ; and in certain oceanic 

 regions they are met with in almost incredible 

 profusion. Their delicate and transparent 

 forms, their elegant tints, and their unrivalled 

 phosphorescence render them the most beau- 

 tiful of Molluscs, and objects of admiration to 

 the naturalist and the voyager. Mr. Bennett 

 relates that, during a voyage to India, the 

 ship, proceeding at a rapid rate, continued 

 during an entire night to pass through distinct 

 but extensive fields of these Molluscs, float- 

 ing, and glowing as they floated, on all sides 

 of her course. Enveloped in a flame of bright 

 phosphorescent light, and gleaming with a 

 greenish lustre, the Pyrosomes, seen at night, 

 in vast shoals upwards of a mile in breadth, 

 and stretching out till lost in the distance, 

 present a spectacle the glory of which may be 

 easily imagined. The vessel, as it cleaves the 

 gleaming mass, throws up strong flashes of 

 light, as if ploughing through liquid fire, which 

 illuminates the hull, the sails, and the ropes 

 with a strange unearthly radiance. 



Genus Pyrosoma, Peron. Common body 

 semi-cartilaginous, floating, cylindrical, 2 to 14 

 inches long, ^ to 3 inches in circumference ; 

 bearing externally numerous pointed pro- 

 cesses, hollow and mammillated within, and 

 open at one of its extremities only. Animals 

 associated in a verticillate arrangement, having 

 two orifices, one at each extremity ; elongated, 

 fusiform, tapering at the outer, and obtuse at 

 the inner extremity ; 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 accord- 

 ing to species, so that the whole forms the 

 long cylinder above described. 



MONOCHITONIDA. Family SALPID^:, 

 Forbes. Synonyms : Salpce, Auct. ; Thalides, 

 pars, and Lucies simples, Savigny ; Biphores, 

 Brugiere ; Biphoridte, MacLeay; Tuniciers 

 fibres, pars, Lamarck ; " les isolees," pars, Cuvier; 

 Salpacea, pars, and Salpiens simples, Blainville ; 

 Salpiens, Van Beneden. The Salpians are free, 

 swimming in the ocean ; plentiful in the Me- 

 diterranean and the warm parts of the ocean ; 

 occurring also occasionally in the Norwegian 

 and North British seas. In shape they re- 

 semble a short and wide tube, sometimes oval 

 or cylindrical, sometimes more or less square 

 in its transverse section, and varying consi- 

 derably in size according to species, from half 

 an inch to 8 or 10 inches in length. 



The test is thin and transparent, open at 

 the ends and often supplied with terminal and 

 lateral processes. The mantle lines the test, 

 and is more or less adherent throughout ; its 



interior constitutes the branchial cavity ; it is 

 provided at one of the terminal openings with 

 a more or less perfect valvular apparatus; and 

 contains a branchial fold traversing it obliquely. 

 Near one extremity the chief viscera are 

 grouped together into a conspicuous mass 

 (the " visceral nucleus" of authors), to which 

 the brilliant tints of the liver usually impart 

 an orange, brown, or reddish hue {jig. 772.). 



Fig. 772. 



Salpce, isolated and associated. 



A. $. runcinata, solitary; B. S. runcinata, asso- 

 ciated ; c. 8. zonaria, aggregated. 



This family is of considerable interest on 

 account of their singular mode of reproduc- 

 tion, discovered by Chamisso, and on account 

 of the philosophical generalisations partly 

 founded thereon by Steenstrup. These ani- 

 mals occur under two distinct conditions, 

 being at one time solitary, and at another as- 

 sociated into circular or lengthened groups 

 termed garlands, cordons, ribands, and chains 

 {fig. 772. B and c). The Salpa-chains, vary- 

 ing in length from a few inches to many 

 feet, swim through the tranquil water with 

 a regular serpentine movement, and are often 

 regarded by sailors as sea-serpents ; but when 

 taken from the water the individuals of the 

 group are easily detached. Thus, in conse- 

 quence of accidents, separate members of these 

 chains are often met with in seas abounding 

 with these Molluscs ; but other, separate, 

 Salpce are also met with that have never been 

 united to others, and differ considerably in 

 form from the associated ones (fig. 772. A). 



Chamisso, however, discovered that such 

 permanently solitary Salpce do not belong to 

 species distinct from those united in chains, 

 however dissimilar (and they are usually so 

 dissimilar as to appear even generically dis- 

 tinct), but are either the parents or the pro- 

 geny, as the case may be, of the aggregate 

 forms ; and that chained Salpce do not produce 

 chained Salpce, but solitary Salpce, which in 

 their turn do not produce solitary, but chained 

 SalpcE. Consequently, as Chamisso graphi- 

 cally observed, "a Salpa- mother is not like 

 its daughter or its own mother, but resembles 

 its sister, its grand- daughter, and its grand- 

 mother."* 



This family is mainly represented by the 



* Forbes, British Molluscs, p. 48. 



