COMMON EEL. 
1025 
the young having, as usual, comparatively larger eyes 
partly in connexion with the different environments and 
habits of the fish, and partly owing to the above-men- 
tioned retrogressions of development, considerable varia- 
tions appear in the relative dimensions of the eyes. In 
young Eels (sometimes even in specimens 37 2 dm. long) 
and in the variety known as latirostris, the longitudinal 
diameter of the eyes is about equal to the interorbital 
width or at least 3 / i thereof. The eyes are compara- 
tively smallest, as a general rule, in the migrating Eels, 
usually measuring less than 2 / 3 (sometimes only about 
43 %) of the interorbital width. In the last-mentioned 
specimens the interorbital width is also hardly less" 
than the length of the snout, in the former sometimes 
scarcely 3 / 4 thereof, though the percentage for this re- 
lation increases with age. Each nostril in the pos- 
terior pair lies, in the form of a dermal fissure, set 
obliquely or in the longitudinal direction of the snout, 
just before the upper anterior corner of each eye; the 
anterior nostils are situated, in the form of dermal 
tubes, one on each side of the tip of the snout. The 
mouth is horizontal, with the tip of the lower jaw more 
or less prominent — most distinctly in old Eels and in 
latirostris — and with the corner situated below the eyes 
or, especially in latirostris , somewhat behind the per- 
pendicular from the hind margin thereof. The lips are 
double, fleshy, and tumid, the outer folds being more 
or less expanded at the sides, in the upper jaw as though 
the free maxillaries of other Teleosts were here replaced 
by this dermal growth; but the underlips are usually 
broadest. The length of the upper jaw (of the cleft of 
the mouth), from the tip of the snout to the hind mar- 
gin of the buccal corners, measures about 26 — 33 %, 
that of the lower jaw about 35 — 47 % b , of the length 
of the head, the latter proportion in each case being 
characteristic of latirostris. The dentition of the mouth 
is partly described above. The most characteristic point 
in the dentition of our Eel, as opposed to East Indian 
and Australian forms otherwise very closely resembling 
it, is the absence in the jaw-cards of the longitudinal, 
toothless gap shown by the last-mentioned forms, though 
the innermost row in both jaws, even in the European 
Eel, is made up of smaller teeth, and may, as a rule, 
be distinguished more easily than the others. The 
tongue is fleshy, free, toothless, and elliptical, with a 
small, short tip. Gill-rakers and p s eu d o b ranch i aa are 
wanting. The fine and pointed pharyngeal teeth, weaker 
than the jaw-teeth, form dense, velvety cards, two above, 
of an oval shape, on the upper pharyngeals, and two 
below, of a more elongated shape, on a thin inward 
expansion of the lower pharyngeals, which else resemble 
branchial arches. The upper half of the gill-openings, 
which are slit-like or curved forwards in a crescent, 
lies just in front of, the lower half below the base of 
each pectoral fin, their height being equal to this base 
and about the same as the interorbital width. 
The dorsal tin is of about uniform height, though 
low in front and very gradually increasing in height 
behind, the increase being proportioned to the percep- 
tible decrease in depth shown by the posterior third of 
the body. The longest rays, which measure about V 2 
— 2 / 5 of the greatest depth of the body, thus lie in the 
hindmost part of the fin, just before it slopes to form, 
together with the caudal and anal fin, a lanceolate tip 
at the end of the tail. The anal fin is similar to the 
dorsal, but much shorter, commencing, as we have men- 
tioned, considerably further back, so that the distance 
between the dorsal fin and the tip of the snout is about 
70 — 75 % of that between the anal fin and the same 
point. In Eels 2 1 / 2 — 7 dm. long this difference increases, 
as a rule, during growth, until the body attains a length 
of about 47 2 dm., but afterwards diminishes, the length 
of the head thus being generally less in middle-sized 
specimens, especially in the migrating Eels, than this 
difference, in large Eels somewhat greater than the 
same. But the individual variations appear to deprive 
the difference of all systematic significance; nor does 
it seem to possess any importance as an external sexual 
character. 
The pectoral fins, when expanded, are oval, often 
somewhat pointed, and the middle rays (about the 10th) 
are the longest. The relative length of these fins ex- 
presses both a distinct alteration of growth, the young 
having even relatively shorter pectoral fins than the 
old, and a difference of sex, the males in general having 
shorter pectoral fins than the females. In 6 Eels (4 cd 
and 2 ?) 23 — 41 cm. long the average length of the 
pectoral fins proved to be 3'6 % of that of the body 
and 8"6 % of the distance between the anal fin and 
the tip of the snout. In 7 Eels (all ?) 45 — 68 cm. 
a According to Jacoby even greater. 
6 According to Kroyer up to 54 /. 
