1020 
SCANDINAVIAN FISHES. 
appearance, of l-obulate organs (Sw. flikorgan , Germ. 
Lappenorgan). They consist of a row of rounded la- 
mella;, coherent to each other just at the base, and 
suspended from the efferent duct ( vas deferens). 
In their internal structure the ovaries show a mesh- 
work of connective tissue, so closely packed, when they 
are unripe, with strongly refractive fat-globules, that it 
is difficult enough to distinguish among these the ex- 
ceedingly small eggs, which in the common Eel usually 
measure during the summer months at most about 1 / 10 
mm. in diameter, and late in autumn or even in De- 
cember attain a size of about 1 / i mm. The testes are 
essentially similar to the ovaries in the texture of their 
stroma (connective-tissue fold), but are without adiposis, 
being consequently more transparent and difficult of 
detection. Most easily perceptible is their white efferent 
duct ( vas deferens). Their seminal cells (spermatogonia) 
are also exactly similar at first to newly-formed ova, 
and remain extremely small, measuring 0.015 — 0.03 
mm. in diameter; but they multiply by fission as they 
pass from the germinal epithelium into the stroma, 
where they gather in their special cavities (spermatic 
ducts). In the Conger and Mu ram a the development of 
the spermatozoa has been traced; in the common Eel 
spermatozoa have not yet been observed. 
Some Enchelymorphs, among them probably our 
common Eel", develop without any great metamorphosis. 
Others, such as the Conger, have a larval existence dur- 
ing which they are scarcely recognisable. These larva; 
Avere first described under a generic name, Leptoceplia- 
lus b or Hehnichthys c , and were long regarded as types 
of a distinct family Leptocephalidce or Helmiclitkyidce) 
or even of an order ( Lemniscatf ). The structure of 
these larvm was described by Kolliker in 1852b They 
are thin (ribbon-shaped) or more terete (cylindrical), 
and so transparent that only the black eyes with sil- 
very iris betray their presence, as they move Avith sIoav 
and languid undulations of their Avhole body, sometimes 
near the coast, sometimes in the middle of the ocean. 
The head is extremely small — hence their name 7 — 
and the skeleton most feebly developed, Avith hardly 
any signs of vertebras, these being confined, as a rule, 
to the hindmost part of the body. The notochord 
( chorda dorsalis), entire or only marked Avith annular 
constrictions, advances Avithout a break into the carti- 
laginous mass of the skull, and lies in the body, en- 
closed, together Avith the spinal cord and the great 
blood-vessels, in a mucous mass. Avhich separates these 
parts from the surrounding musculature. The muscular 
mass is fastened to the skeleton only in front (at the 
head) and behind (at the tail), being attached elseAvhere 
to the skin; but it is divided, as in other fishes, by 
the zigzag transverse bands ( myocommata ) into flakes 
{myomeres), each Avith an angle (directed forwards) 
at the middle of the sides of the body, another (di- 
rected backwards) at the back, and a third at the 
ventral margin. The mouth is armed, both in the 
upper jaAv and the loAver, Avith comparatively large and 
strong, rather scattered, straight arid pointed teeth, set 
in a single toav and directed obliquely fonvards. Each 
nasal cavity is a depression in front of the eye, Avith- 
out proal nostril. The tubular abdominal cavity ex- 
tends along the greater part of the ventral margin. 
The straight digestive canal includes, according to Kol- 
liker, a caecum-like stomach, Avith two upward, caecal 
diverticula and two similar appendages belonging to 
the intestine. The liver is faintly developed; spleen, 
air-bladder, and sexual organs are wanting. From this 
larval structure Facciola 5 ' has succeeded in tracing a se- 
ries of transition-forms that bring it to perfect identity 
Avith the young of the Congers, a metamorphosis at 
which Gill 7 ' had already hinted. The most singular 
point is, hoAvever, that these larvae, retaining the struc- 
ture proper to their first stage of development, can 
attain dimensions considerably greater than those of 
the stages in Avhich the terete type and internal struc- 
a In the Ball. Accad. Gioen. Sc. Nat. Catania (Fasc. 34 — 35; Nov. 1893 e Genn, 1894, p. 4) Gbassi and CalandRticcio have ex- 
pressed the supposition that the ova of Anguilla vulgaris are to he found floating in the sea, and that Leptocephalus brevirostris is the 
larval stage of this species. 
b Ghonovii Zoophylac., Fasc. I (1763), p. 135. Morris, an acquaintance of Pennant’s, had found these fishes in St. George’s Chan- 
nel, off Holyhead, North Wales. 
c Rakinesque, hid. Ittiol. Sic., where the name is, however, written Helmictis. 
d Richardson. 
e Zeitsclir. f. Wiss. Zool., Bd IV, p. 360. 
f From Gr. Xercvog, fine, small, and VXqtaXf head. 
■' II Naturalista Siciliano, Anno XII (1893), p. 194. 
h Proc.. Acad. Nat. Sc. Philad. 1864, p. 207. 
