314. ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
With respect to the striking property which gave rise to the name 
conferred on the genus, Péron asserts that the Pyrosomata exhibited 
movements of alternate contraction and dilatation at regular intervals ;. 
and that each contraction was accompanied by the development of a 
luminosity, which, when at its brightest, was red, but, in dying away, 
passed through shades of orange, green, and blue. The light was 
developed upon irritation, and entirely ceased with the animal’s death. 
The only indication of locomotive power was the regular contraction 
just described, whose necessary effect was a slight retrogressive 
movement, in consequence of the reaction of the water forced out of 
the open end of the Pyrosoma. 
In 1815, Lesueur, having previously, as he states, described and 
figured a new species (P. elegans) in the ‘Nouveau Bulletin de la 
Societé Philomatique’ for 1813, added a number of important details. 
to Péron’s account in his ‘ Mémoire sur l’organisation des Pyrosomes, 
et sur la place quils doivent occuper dans une classification naturelle,” 
and showed that Lamarck was in error in assigning to Pyrosomaa 
place near Beroé, the animal being, in reality, a mollusk closely allied 
to Salpa (2. ¢. p. 420). iS 
The species described by Lesueur was named by him P. gigantenim, 
and was obtained in the Mediterranean, near Nice. 
Pyrosoma- giganteum, says Lesueur, has the general form common 
to the two other species; it is transparent, of a-starchy blue colour, 
soft and gelatinous, though slightly coriaceous; its only aperture, 
placed at the upper end, is bounded by tubercles, and provided with 
a membranous expansion, which in certain cases serves to close it. 
The whole body is covered externally with tubercles, but these are 
not disposed regularly like those of Pyrosoma elegans ; they vary in 
their dimensions, some being short and indistinct, while others are 
greatly developed. The largest are conico-cylindrical, flattened and 
lanceolate at the extremity (while those of P. atlanticum are simply 
conical), with a small aperture situated upon that side which looks 
towards the bottom of the sac: this lanceolate extremity is notched 
on its sharp edges, and presents below, between its pointed extremity 
and the opening of which we have just spoken, a small but very 
prominent keel. The inner surface of the Pyrosoma is smooth, 
and provided with a great quantity. of little apertures, each of 
which corresponds with one of the tubercles, and is only the anterior 
end of a canal, whose posterior aperture is placed at the free 
extremity of the tubercle,—a fact easily demonstrated by pouring 
1 Read to the Société Philomatique de Paris on the 4th of March, 1815, and published in. , 
the ‘Journal de Physique’ for June of the same year. 
