EEL-FISHES. 
1019 
above-mentioned folds of adipose membrane, the right 
beginning farther forward than the left, but not ex- 
tending so far back. The structure and significance 
of these organs, especially in our common Eel, has 
long been an obscure question, which was not eluci- 
dated until recent times. 
From the preceding pages (p. 829) we know that 
the Salmonoid family and some other fishes, among 
them the family of the Eels, are destitute of oviducts, 
at least closed ones, such as appear in the remaining 
Teleosts, and that the eggs of these fishes fall, when 
ripe, loose into the abdominal cavity, whence they are 
expressed through a more or less developed peritoneal 
canal on each side, opening into the genital pore just 
behind the vent or into the urogenital aperture com- 
mon to the genitals and the urinary bladder. The 
testes, on the other hand, are furnished, even in the 
Eels, with efferent ducts ( vasa deferentia), which have 
tsc rc tdc ura tel vd d 
hand, they occupy as caudo-abdominal cavities the same 
relation to the skeleton as the abdominal cavity proper. 
The peritonea] fold in which the intestine is suspended 
( mesenterium ) crosses from the intestine to the urinary 
bladder, which lies behind the rectum — leaving in the 
females a triangular opening (peritoneal canal) between 
the lowest part of the rectum and the neck of the 
bladder — and is continued backwards in the middle 
of the haemal canal (or a little obliquely). It thus forms 
a partition wall between the two caudo-abdominal ca- 
vities, suspended from a continuation of the peritoneum 
proper, which lines the walls of these cavities and di- 
vides them from the superposed prolongations of the 
kidneys (caudal kidneys). The most striking peculiarity 
in the generative organs of the common Eel is, how- 
ever, the duplication of the parts contained in the 
caudo-abdominal cavities, each organ consisting there 
of two blades running side by side. 
ra t vd 
t 
B 
Fig. 273. Portions of the testes in Anguilla vulgaris. A , abdominal cavity (posterior part) and caudo-abdominal cavity, opened and with 
the walls folded back to show the enclosed organs; natural size; after Brock. B , a portion of the young testes, at an early stage of deve- 
lopment, in an Eel 23 cm. long, taken at Trollhattan in 1848; magn. about 8 diam., to show how the testicular lobes ( t ) originate in a thin 
and transparent mesorchial fold (at first of uniform breadth) of the peritoneum. 
ts, left, tel, right testicle in the abdominal cavity; tsc, left, tdc , right testicle in the caudo-abdominal cavity; vds , left, veld, right testicular 
duct ( vas deferens)', vs, seminal vesicle; vu, urinary bladder; ra, abdominal, rc, caudo-abdominal divisions of the kidneys; ura , abdominal, 
lire, caudo-abdominal urethra; r, rectum, detached and laid to the left; ved, vena cava dextra; cl, cloaca (emits). 
their common aperture, as usual, in the anterior wall 
of the neck of the urinary bladder. Characteristic of 
the majority of the Enchelymorph genera, but most 
developed in our common Eel, are two backward pro- 
longations of the abdominal cavity and the continua- 
tions in these cavities of the generative organs, one 
below each side of the caudal (post-anal) prolongations 
of the kidneys. We have indeed seen a similar pecu- 
liarity in the Flounders, though the secondary abdo- 
minal cavities are there situated outside the hasmal 
canal (see above, pp. 370 etc.). Here, on the other 
The ovaries have the appearance of frilled bands; 
but their inner (median) side is smooth, and the ap- 
pearance of frills is caused by elevated, transverse (ver- 
tical), simple or double, foliate lobules (ovarial lamella?, 
in which the eggs are developed) on the outer (lateral) 
side, though so arranged that in the caudo-abdominal 
part of the ovary the inner blade has these lobules on 
its inner side, and turns its smooth side outwards, to 
face the outer blade of the same ovary. The testes, on 
the other hand, so long as their real nature was un- 
known, bore the name, conferred on them for their 
