Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/1239/
TUNIC AT A. 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 the}' ge¬ 
nerally contain but a single one, it is still 
highly probable that gemmiparous reproduc¬ 
tion obtains with these animals ; the fissi- 
parous mode, however, imagined by Péron 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 
fdaments 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 (Jig. 786. B, c), may be the 
proliferous stolons as yet untraced throughout 
their course. 
Phosphorescence of Pyrosoma. — M. Péron, 
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 Mémoire 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 millimètre 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° 4V N., long. 11°56'W., and lat. 4° 8., 
long. 18° W., differ but slightly from M. 
Péron’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 
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