274 
MALACOPTERYGII. — MUR^NADiE. 
tinuous all round the tail. The dorsal commences 
at a considerable distance behind the insertion of 
the pectorals. The gill-opening is a small slit on 
each side, situated just at the base of the pectoral. 
The upper jaw is shorter than the lower ; the 
mouth is furnished with small teeth in each jaw, 
and a few at the front part of the vomer. The 
whole body is covered with a thick, smooth skin, 
well supplied with a slimy mucous secretion. The 
intestine is long but straight ; the air-bladder is 
also long, and furnished near its middle with a 
peculiar gland. A curious pulsating sac has been 
recently discovered in the tail of the Eels, with 
regular beats, quite independent of the action of 
the heart ; the object of this organ is the circu- 
lation of lymph, a thin colourless fluid, having 
much of the nature of blood, deprived of its 
colouring disks. Similar organs have been ob- 
served to exist in some Reptiles, particularly 
Amphibia, 
The Eels are properly fresh-water fishes, which 
migrate to the sea after they have deposited their 
spawn in the rivers. We have three or four 
species, differing a little in the form of the head, 
but sufficiently alike both in appearance and 
habits to allow of one being taken as a fair sam- 
ple of the rest. The most common is the Sharp- 
nosed Eel {Anguilla acutirostris, Yarr.), which 
is abundant in most of our rivers, lakes, and 
marshes, as in those of continental Europe. In 
the waters of high mountains, however, and in 
countries subject to severe winter’s cold, the Eel 
is not found, as it cannot endure a very low 
temperature. During intense frosts, accom- 
panied by a piercing east wind, thousands of 
