TUNICATA. 



1229 



recognised by the form and arrangement of 

 their double branchiae. 



Whether the ova of Pyrosoma be always 

 composed of four, or a greater or less number 

 of young individuals, or whether they ge- 

 nerally contain but a single one, it is still 

 highly probable that gemmiparous reproduc- 

 tion obtains with these animals ; the Jissi- 

 parous mode, however, imagined by Peron as 

 possibly occurring in the adult Pyrosome, is 

 totally unsupported by evidence. The several 

 stages of development in which the individual 

 animals are found to exist in the common 

 mass of the test, as noticed by Savigny, point 

 to this conclusion ; and possibly the delicate 

 filaments regarded as muscular fibres by Sa- 

 vigny, first pointed out by the acute observer 

 of these creatures, Lesueur, as traversing the 

 test in a line with the abdominal cavities of 

 the adult animals (fig. 786. B, c), may be the 

 proliferous stolons as yet untraced throughout 

 their course. 



Phosphorescence of Pyrosoma. M. Peron, 

 who first discovered and established the genus, 

 has given a lively description of the circum- 

 stances under which the P. atlanticum were 

 first met with by him, in his Memoire sur le 

 Pyrosome. * " We had," says he, " for a long 

 time been detained by calms in the equatorial 

 regions, between 19 and 20 long, west of 

 Paris, and 3 and 4> north lat., the temperature 

 of the sea being at the surface 22 Reaumur ; 

 and we could make no progress except by the 

 aid of the short-lived storms peculiar to these 

 climates. In the evening of the 13th Frimaire 

 we experienced one of the strongest of these 

 squalls ; the sky was on all sides loaded with 

 heavy clouds ; all around the obscurity was 

 profound ; the wind blew violently; and the 

 ship cut her way with rapidity. Suddenly 

 we discovered, at some distance, a great phos- 

 phorescent band stretched across the waves, 

 and occupying an immense tract in advance 

 of the ship. Heightened by the surrounding 

 circumstances, the effect of this spectacle was 

 romantic, imposing, sublime, rivetting the at- 

 tention of all on board. Soon we reached 

 the illuminated tract, and perceived that the 

 prodigious brightness was certainly and only 

 attributable to the presence of an innumerable 

 multitude of largish animals floating with the 

 waves. From their swimming at different 

 depths they took apparently different forms ; 

 those at the greatest depth were very inde- 

 finite, presenting much the appearance of 

 great masses of fire, or rather of enormous red- 

 hot cannon-balls ; whilst those more distinctly 

 seen near the surface perfectly resembled in- 

 candescent cylinders of iron. 



" Taken from the water, these animals per- 

 fectly resembled each other in form, colour, 

 substance, and the property of phosphores- 

 cence, differing only in their sizes, which 

 varied from 3 to 7 inches. The large, longish 

 tubercles with which the exterior of the Pyro- 

 somes was bristled were of a firmer substance 

 and more transparent than the rest of the 



* Annales du Museum d'Hist. Nat. tome iv. 1804. 



body, and were brilliant and polished like 

 diamonds. These were the principal seat of 

 phosphorescence. Between these large tu- 

 bercles, smaller ones, shorter and more ob- 

 tuse, could be distinguished ; these also were 

 phosphorescent. Lastly, in the interior of 

 the substance of the animal, could be seen, 

 by the aid of the transparency, a number 

 of little, elongated, narrow bodies (viscera), 

 about a millimetre in length, which also 

 participated in a high degree in the possession 

 of the phosphoric light. 



" The colour of the animals, when at rest 

 or when moribund, was observed to be of an 

 opaline yellow, mingled with a disagreeable 

 green ; but during the spontaneous contrac- 

 tions of the animals, and which were also 

 easily excited at the pleasure of the observer, 

 the body seemed to burn, becoming instantly 

 like molten iron, with an extremely bright 

 light ; but, as the phosphorescence again 

 ceased, the colour of the animal passed suc- 

 cessively through a number of extremely 

 agreeable, light, and varied tints, such as 

 red, yellow, orange, green, and azure blue, 

 the last shade being extremely lively and pure. 

 "Left to itself in a glass of sea- water, the 

 Pyrosome exhibited at regular intervals of 

 time a slight alternating movement of con- 

 traction and dilatation. In these movements, 

 the phosphorescence was seen to be deve- 

 loped during the contraction, then to grow 

 insensibly feebler, and entirely disappear, 

 until in the next contractile movement it was 

 quickly re-established. 



" By often irritating the animal, either by 

 touching it or by shaking the water in which 

 it floated, the phosphorescence could be ex- 

 cited and maintained for a much longer time. 

 Evidently dependent on the organisation and 

 the life of the individual, after death, as is 

 the case with all other phosphorescent marine 

 animals, it could not be reproduced." 



We may remark that the observations 

 made by Mr. F. D. Bennett*, who more than 

 once met with shoals of P. atlanticum in lat. 

 1 41' N., long. 11 56' W., and lat. 4 8., 

 long. 18 W., differ but slightly from M. 

 Peron's notices of the same animal. The 

 former observed, that when the specimens 

 were taken in the hand from a vessel of sea- 

 water, the whole mass of the animal became 

 instantly illuminated by myriads of bright 

 dots, much resembling in hue the points on the 

 wing-cases of the diamond-beetle ; and that the 

 small specks of a brown or red colour, that 

 were imbedded in the general tissue, and in- 

 termingled with the prominent, rigid, pearly 

 tubercles, appeared to him to be the chief 

 seat of the phosphoric light, frequently re- 

 maining bright, whilst the remainder of the 

 body exhibited only its naturally white or 

 yellowish hue a hue which changed after 

 death into a red tinge. In making a close 

 examination of the animal, Mr. Bennett re- 

 marked that no luminous matter was com- 

 municated from the surface of the animal to 



* Proceedings of the Zoological Society, 1833 

 and 1837. 



