18 M ED 
while the animal is fvvimming, that they appear like 
the continual paflage of a fluid along the ribs. When 
the animal fwarn gently near the furface of the water, 
its whole body became occaflonally illuminated in a flight 
degree; during its contractions, a ftronger light iffued 
from the ribs; and, when a fudden fhock was communi¬ 
cated to the water in which feveral of thefe animals were 
placed, a vivid flafli was thrown out. When the body was 
broken, the fragments continued luminous for fome fe- 
conds, and, being rubbed on the hand, left a light like 
that of phofphorus; this, however, as well as every other 
mode of emitting light, ceafed after the death of the 
animal. 
In the month of September 1806, Mr. Macartney 
caught at Sandgate, and in April 1809 at Haftings, a 
number of thefe fame animals. They were of various 
flzes, from about the half of an inch in length, to the 
bulk of the head of a large pin. Many of them ad¬ 
hered together in the fea; lome of the larger fort were 
covered with fmall ones, which fell off when the animals 
were handled, and by a perfon unaccuftomed to obferve 
thefe creatures would have been taken for a phofphoric 
fubftance. On putting a number of them into a glafs 
containing clear fea-water, they (till fliowed a difpofuion 
to congregate upon the furface. It was obferved that, 
when they adhered together, they fhowed no contractile 
motion in any part of their body, which explains the caufe 
of the pale or white colour of the diffufed light of the 
ocean. The flaflies of light which Mr. Macartney faw 
come from the fea at Herne-bay, were probably produced 
by a fudden and general effort of the medufae to feparate 
from each other, and to defcend in the water. 
2. Medufa pileus : body globular, with ciliate ribs, and 
two ciliate cirri. Inhabits the Mediterranean ; and is 
perhaps the luminous fpecies defcribed by Forfkal under 
the name of Medufa denfa. 
3. Medufa cucumis : oblong with eight ciliate ribs, and 
cirri. It is found in the Greenland feas, and moves very 
ilowly by means of the fibres on the ribs: when touched, 
it contracts itfelf into the form of an apple. The body 
is white mixed with blue, and covered with irregular red 
fpots: it has two apertures, terminal meeting in the ob¬ 
long middle cavity. 
4. Medufa ovum : ovate, with eight ciliate ribs and two 
pair of cirri, one pair very long. Inhabits the Greenland 
feas; and is about the fize of a pigeon’s egg. The body 
is lucid, and extremely fragile; the fragments, while 
alive, are blue. 
II. Body fmooth. 
5. Medufa porpita: flat above, beneath a little convex, 
grooved, and villous. It is found in India. 
6. Medufa cruciata: body marked with a milk-white 
crofs. It has the appearance of a tranfparent colourlefs 
jelly; the body is furrounded at the margin with very 
fine fibres: the crofs is marked with a brown fpot on each 
arm. It is luminous when under fun-fhine. Inhabits the 
feas of Europe. 
7. Medufa hyfocella : convex above, with fixteen rays, 
.and four united tentacula beneath. Found in the fea 
round Portugal. The body above is whitilb, the rays 
sompofed of extremely-minute reddilh-brown dots; be¬ 
neath it is concave ; the tentacula are longer than the 
body, lanceolate, and marked with reddifh (triae. 
8. Medufa sequorea: flattifh, with a villous infleded 
tentaculate margin. It is extremely fimple, foft, and 
fringed at the margin with white. 
9. Medufa hemifphasrica: hemifpherical, with four tranf- 
verfe ribs beneath, and marginal tentacula and globules. 
It inhabits the European leas; and is about two lines in 
diameter. This fpecies is reprefented in the Helmin¬ 
thology Plate III. fig. 2. p. 350. vol. ix. of its natural 
fize, (fprming a vail contrail with the cuttle-fifli on the 
Jame plate;) and magnified at fig. 3. 
Whales are faid to feed chiefly upon this and fome 
U S A. 
other fpecies of Medufa. Their gelatinous texture mud 
render them extremely nourilhing, and favour the pro¬ 
duction of oil, for which the cetaceous tribe is fo ex¬ 
tremely valuable; but a vail number of thefe little unfor¬ 
tunate unoffending creatures multperifli to afford a meal 
for a whale. 
This appears to have been another of the luminous 
fpecies difcovered by Mr. Macartney, at the fame time 
with the M. infundibulum. The animals were of a very 
faint purple colour; the largeft individuals meafured about 
three quarters of an inch in diameter. The margin of the 
umbrella was undivided, and furrounded internally by a 
row of pale brown fpots, and numerous fmall twilled tenta¬ 
cula: four opaque lines crolfed in an arched manner from 
the circumference towards the centre of the animal; an 
opaque irregular-fhaped procefs hung down from the mid¬ 
dle ofthe umbrella; when this part was examined with a lens 
of high powers, it was difcovered to be inclofed in a flieath 
in which it moved, and that the extremity of the procefs 
was divided into four tentacula, covered with little cups 
or fuckers like thofe on the tentacula of the cuttle-fi/h. 
This fpecies bears a ftriking refemblance to the figures 
of the M. bemifpherica publifhed by Gronovius 3 and 
Muller; indeed it differs as little from thefe figures as 
they do from each other. Its luminous property, how¬ 
ever, was not obferved by thefe naturalifts, which is the 
more extraordinary, as Muller examined it at night, and 
fays it is fo tranfparent, that it can only be feen by the 
light of a lamp. If it fltould be dill confidered as a dif- 
tin£l fpecies, or as a variety of the bemifpherica, Mr. Ma¬ 
cartney propofes to call it M. lucida. In this fpecies, the 
central part and the fpot round the margin are commonly 
feen to fliine on lifting the animal out of the water into 
the air, presenting the appearance of an illuminated wheel; 
and, when it is expofed to the ufual percuffion of the wa¬ 
ter, the tranfparent parts of its body are alone luminous. 
The following experiments were made upon fome of 
thefe worms: 
1. Some hemifpherical medufae were put into a fpoon, 
containing a fmall quantity of fea-water, and held over a 
burning candle. As foon as the water became heated, the 
medufae appeared like illuminated wheels, the fpots at the 
margin and centre alone emitting light; in which man¬ 
ner they flione vividly and permanently for about twenty 
feconds, when they lhrunk and died, after which they 
were no longer luminous. 
2. Some of the fame fpecies were put into fpirits : a 
11 rong and unremitting light was inllantly given out, which 
iffued from the central and marginal parts, as in the pre¬ 
ceding experiment, and continued until they died. 
3. Some of the fame fpecies, contained in a fmall glafs 
jar, were introduced into the receiver of an air-pump, and, 
the air being exhaulted, they flione as ufual when Ihaken : 
if any difference could be perceived, the light was more 
eafily excited, and continued longer, in vacuo. 
4. A fingle worm was placed in a fmall glafs difli, con¬ 
taining a quantity of water, merely fufficient to allow the 
animal to preferve its figure: being infulated, it was elec¬ 
trified, and fparks drawn from it, which had not the 
flighteff effefl. The experiment was repeated feveral 
times with different individuals, but without exciting the 
animals to throw out light. 
5. Some hemifpherical medufae were placed in contact 
with the two ends of an interrupted chain, and flight 
electric ftiocks paffed through them. During the very 
moment of their receiving the fhock, no light wasvifible; 
but immediately afterwards they flione like illuminated 
wheels, which appearance remained for fome feconds. 
Upon the clofelt infpe&ion with a magnifying glafs, no 
contractile motion could be perceived to accompany the 
exhibition of the light. The application of electricity, 
in this inftance, feems to have aCted merely as a ftrong 
mechanic (hock. 
We may add, that if the light emitted by animals were 
derived 
