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XVI. On the Anatomij and Development of Pyrosoma. Bij Thomas H. Huxley, Esq., 

 F.B.S., F.L.S., Sec. G.S., Professor of Natural Sistory in the Government School 

 of Mines. 



Read December 1st, 1859. 



§ 1. Sistory of the Genus Pyrosoma. 



The genus Fyrosoma was first established in 1804 by Peron, in a memoir* published 

 in the fourth volume of the ' Annales du Museum,' and accompanied by a plate repre- 

 senting the exterior and a longitudinal section of the animal. Peron thus defines the 

 genus and the species which he observed : — 



" Pyrosoma. 



"Corpus liberum, subconicum, extremitate ampliore apertum vacuum, aperturje margine intus tuberculis 

 cincto. 



" Pyrosoma atlanticum. J^Iquatorio-atlanticum, gregarie pelagivagum, viridissime 

 phosphorescens, coloribus eximiis tunc efl'ulgens, in aquis viginti duobus reaumu- 

 rianis calidioribus occurrens, 10-12, 14-16 centrimetros sequans." 



M. Peron's conceptions of the exigencies of a zoological diagnosis were evidently of a 

 singular kind, and his memoir contains not a single observation calculated to throw 

 light upon the true nature of one of the most remarkable animals that has ever been 

 discovered. With respect to the striking property which gave rise to the name conferred 

 on the genus, Peron asserts that the Fyrosomata exhibited movements of alternate con- 

 traction 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 entn-ely 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 Fyrosoma. 



In 1815, Lesueur, having previously, as he states, described and figured a new species 

 (P. elegans) in the ' Nouveau Bulletin de la Soci^te Philomatique ' for 1813, added a num- 

 ber of important details to Peron's account in his " Memoire sur I'organisation des 



* "Memoire sur le nouveau genre Pi/rosoma," par M. Peron. Annales du Museum, tom. iv. p. 437, lSO-1. 

 Forskal's Descriptiones Animalium (177o) contains the following passage : — 

 " 29. Medusa BuRois. Tres ejus varietates vidi vel species. * * * * * 



"29c. RUFESCENS: ovato-oblonga ; ssepe 5 poll, longa ; intus prorsus vacua. G&llice, Concoml/re de la mer. In 

 mari Mediterraneo frequens." 



Was Medusa Ber'Oe rufescens a Pyrosoma 1 



VOL. XXIII. 2 1) 



