3 



ii 



344 MANUAL OF THE MOLLUSCA. { 



The Pyrosomes are 2 — ] 4 inches long and i — 3 inches in circumference ; ! 



they are composed of innumerable tunicaries united side by side, with their i 



orifices so arranged that the inhalent openings are external, the exhalent inside ] 



the tube, and the result of so many little currents discharged into the cavity \ 



is to produce one general outflow, which impels the floating cylinder with its I 



closed end foremost. ] 



The ganglionic side of each zoid is turned towards the open end of the j 



tube ; the respiratory cavity is large, and completely inclosed by a quad- ! 



rangular net-work ; the test and mantle are united and lined by a vascular \ 

 sinus-system. There is an "endostyle" on the haemal side, as long as the 

 branchial sac. The ventral column (hypo-pharyngeal band) supports a series 

 of languet 



The sexes are combined; reproduction takes place by huds developed 

 amongst the adult zoids, and by solitary ova connected with the inner tunic 

 by a pedicle near the posterior termination of the endostyle ; 2 or 3 ova are 

 perceptible in the young zoid at a very early period. 



The Pyrosomes are often gregarious in vast numbers; in the Mediterranean 



they sometimes abound to such an extent as to clog the nets of the fishermen. ; 



They are phosphorescent at night. The light of P. atlanticum is very vivid \ 



and of a greenish blue colour ; when touched the light appears in very minute j 



sparks, issuing from each of the separate individuals, it first appears at the \ 



part touched, and gradually spreads over the body ; it disappears after death. \ 



{Milller). Placed in a vessel of salt-water, and at rest, they emit no light, ; 



and the light excited by touching them gradually fades after the removal of ' 



ii-ritation ; but immersed in fresh-water they continue glowing with their ; 



brightest refulgence for several hours — as long as life remains. Peron first ! 

 noticed them as " a phosphorescent band, stretched across the waves and 

 occupying an immense tract in advance of the ship. Those most distinctly 



seen resembled incandescent cylinders of iron." Humboldt speaks of the ' 



Pyrosomce as forming a light li feet in diameter, by which the fishes were j 



\'isible I i 



FAMILY Y. Salpidae. \ 



Animals free, oceanic ; alternately solitary and aggregated. j 



Salpa, Forskahl, 1775. '\ 



Etym. Salpe a luminous fish. Spi. Dagysa, Banks and Solander. 



Thalia, Brown. Biphora, Brug. Pegea and Jasis, Sav. 



Ex. S. maxima, PI. 24, fig. 22, solitary form. \ 



Animqil oblong, sub-cylindrical, truncated in front by the oral orifice, ; 

 pointed posteriorly ; anal orifice sub-terminal ; test thin, transparent ; muscu- | 

 lar mantle incomplete, forming a set of transverse or oblique bands ; mantle 

 cavity lined by a system of vascular sinuses ; gill rudimentary, forming an j 



