EEL-FISHES. 
1017 
The third interpretation (3) — according to which 
the margin of the upper jaw consists laterally of the inter- 
inaxillaries and anteriorly of the vomer (there coalescent 
with the ethmoid) — was first- proposed by Cuvier", 
and has long been the most generally accepted. It pre- 
supposes that true maxillaries and palatines are wanting. 
The history of the Eels’ development has not yet- 
pronounced judgment on these three opinions; and a 
fourth explanation might reasonably be suggested, name- 
Iv that the palatines and maxillaries were originally 
independent, but have coalesced, as Meckel and, after 
him, Peters assumed of the relation between the inter- 
maxillaries and the ethmoid and vomer. From the 
evolutional history of the higher vertebrates we know 6 
that the maxillaries as well as the palatine roof are 
primordial excrescences of the mandibular arch, and 
that the incipient palatine roof may appear as a se- 
Fig. 271. Hyoid arch of Anguilla vulgaris. X 3 / 2 . 
A: hyoid arch with branchiostegal rays; B: lingual hone; C: the same, 
seen from below. 
/, lingual; uh, urohyoid; bbr, first copula (basi-branchial); cell, cera- 
tohyoid; eph, epihyoid; 11. hr ., branchiostegal rays. 
condary growth in an inward direction, originating from 
the maxillary arch. Whether an equally intimate rela- 
tion between these parts has possibly arisen during their 
reduction in the Eels, is a question which only the his- 
tory of evolution can solve. We accordingly consider 
it still doubtful whether intermaxillaries and maxillaries 
are wanting in the Eels or have coalesced with more 
internal bones, and in the present state of the question 
the describer is fully entitled to speak of maxillary 
and vomerine teeth. 
In conjunction with the great development of the 
branchial cavity the Eels have very broad branchiostegal 
membranes and long branchiostegal rays (B. hr.). But 
the former are united throughout by far the greater 
part of their margins to the skin and joined to each 
other, thus leaving only small, slit-like gill-openings; 
and all the latter, except the uppermost (hindmost) ones, 
are slender, filamentous, and coiled backwards, upwards, 
forwards, and finally downwards, so as to include within 
their curve both the operculum and the suboperculum. 
In the Conger (fig. 282, p. 1036) the last two bran- 
chiostegal rays of each membrane are expanded at the 
top; in the common Eel (fig. 271) the expansion is con- 
fined to the last ray, but is so great that the ray is 
sometimes equal in breadth to the comparatively nar- 
row, obliquely semi-elliptical operculum (fig. 270, op). 
The sabre-shaped — in the Conger (fig. 282) elongated 
triangular, posteriorly pointed, but curved — suboper- 
culum (sop) follows the curved inferior margin of the 
operculum, and is weaker both in the common Eel and 
the Conger than the triangular, anteriorly pointed inter- 
operculum ( iop ), which is even larger than the thin, 
crescent-shaped preoperculum (pop). 
The Eels are exceedingly voracious; and their di- 
gestive canal is accordingly rather short and simple. 
Our common Eel may serve as an example. The main 
abdominal cavity of this species varies considerably in 
length, between about- 26 and 30 % of the length of 
the body; but- in the caudal part it has on each side 
a prolongation, of which we shall give a- fuller descrip- 
tion when treating of the sexual organs. The thin- 
walled and rather wide oesophagus passes into the sto- 
mach without a break, except that the longitudinal 
folds (ridges) in which the mucous membrane lies on 
the inside become thicker and higher in the stomach, 
while the wall of the stomach is also thicker than that 
of the oesophagus. Straight backwards the stomach is 
prolongated in the form of a cone; but from the right 
and lower side of its anterior part it sends out a pyloric 
portion, with equally thick walls, which runs forward 
to the hind margin of the liver, where it bends abruptly 
in a narrow crook, so that the beginning of the intestine, 
which runs backwards, lies close to its under surface. 
There are no ceecal diverticula. At the middle of the 
crook is a funnel-like valve (an annular fold on the in- 
side), marking off the pylorus from the intestine; and 
on the inside of the latter the mucous membrane is 
disposed in a honeycombed network of deep, confluent 
a Mem. Mus. cl' Hist. Nat., tome I, p. 118. 
h Cf. Smitt, Ur de hogre cljurens utvedclingslnstoria, p. 167. 
