APRIL 16, 1914] 
NATURE 
165 
and, telling us that the Siciliins still call the 
larval eels casentule, that 1s, “earthworms,” 
while the philosopher tells us that the eels spring 
from “earthworms,” yijs évtepa, he inclines to the 
conclusion that Aristotle knew a deal more about 
the biology and development of the eel than is 
actually set forth in his brief recorded references. 
It was Redi, in the seventeenth century, who 
showed, with the utmost clearness, that the eels 
breed out in the open sea, after migrating down 
the rivers “nel rimpunto della luna,” “in the 
dark of the moon.” 
Another chapter of the story opens, just 150 
years ago to a year, when a certain Mr. William 
Morris sent to Pennant, from Holyhead, the curi- 
ous little fish which, in our youth, we used te 
read of in ‘“Yarrell,” under the name of the 
“Anglesey Morris,” or Leptocephalus morrisii, 
as Gronovius had called it. Other similar fishes 
were from time to time described, until in 1856, 
Kaup, in a British Museum catalogue, described 
a number of species, including a certain L. brevi- 
vostris, from the Straits of Messina. A multitude 
of naturalists dealt, during the early part of the 
last century, with these little fishes. Cuvier said 
that their study was ‘une des plus intéressantes 
auxquelles les naturalistes voyageurs puissent se 
livrer.” johannes Miller, with splendid insight, 
declared that they were closely allied to the Mure- 
noids. Carus, in 1861, suspected that they were 
larval forms of some other fish, perhaps Cepola 
or Trichiurus, and in 1864 Dr. Theodore Gill 
asserted that these little Leptocephali were but 
larval eels, a fine instance of zoological prescience. 
A long controversy followed, in which Giinther 
and others maintained that the Leptocephali were 
not an ordinary necessary stage in the life-history 
of the eels, but were abnormal larve, distorted by 
an unnatural habitat. At length it was made clear 
by Dareste, Moreau, and finally and experiment- 
ally by Delage, in 1886, that Leptocephalus 
morrisii was the normal larva of the conger. 
Here begins the series of researches by Grassi and 
Calandruccio, who between 1892 and 1905 con- 
firmed Delage’s account of the metamorphosis of 
the conger, showed that Kaup’s L. brevirostris 
was the larva of the common eel, studied in detail 
the life-history and metamorphosis of a whole 
series of other Leptocephalids, and maintained 
that these little larval fishes were inhabitants of 
the deep waters, from which sometimes, as in the 
Straits of Messina, they were brought up to the 
surface by currents or by whirlpools; just as 
Yarrell told, long before, of a specimen cast up 
in the eruption of Graham’s Island in the Medi- 
terranean. As was foreseen by Salvatore Lo 
Bianco, in 1891, the larve of the common eel are 
inhabitants of the deep sea, and three years later 
Johan Petersen captured the Leptocephalus of the 
common eel, L. brevirostris, out in the Atlantic, 
south-west of the Faeroe Islands. From that date 
onwards, together with Prof. Grassi himself, a 
band of Scandinavian  naturalists—Petersen, 
Hjort, with his pupil Einar Lea, and last but not 
least, Dr. Johann Schmidt—have carried on the 
investigation of the metamorphosis and migra- 
NO. 2320, VOL. 93] 
tions of the eel.2. Schmidt, Hjort, and Lea have 
now shown that the main breeding-place of the 
eel isnot only out in the open Atlantic, but is in 
all probability in the warm and very salt waters of 
the southern part of the North Atlantic, south and 
west of the Azores; and an interesting part of 
Mr. Lea’s paper is one in which he discusses 
the probable duration of the eel’s long voyage to 
its breeding-place, and of the slow return of the 
young larvee home. This point is further eluci- 
dated by Dr. Bowman, who is able to trace the 
Leptocephali of the common eel on their way 
round the west and north of Scotland from about 
| June to August, while by November or December 
| they appear as “elvers” off the coast, and are 
ready to ascend the rivers in March or April. The 
Leptocephali of the conger are found off the east 
coast from December to May. 
But there still remain a few points of doubt, 
and therefore of controversy, on which the learned 
Italian naturalist and his Scandinavian brethren 
do not quite agree. These are questions which 
we would not lightly judge or prejudge, and we 
may simply say that Dr. Grassi seems to state 
his case with great fairness, and -with a 
very open mind. -Among the points still at issue 
we may mention two. First, does the eel breed 
in the Mediterranean? And secondly, are the 
Leptocephali (at least those of the common eel) 
_ inhabitants of the surface-waters, of the bottom, 
or of intermediate depths? Dr. Schmidt believes 
that the eel does not propagate at all in the 
Mediterranean, “‘conclusione molto sorprendente,” 
as Grassi calls it. He holds that for the Mediter- 
ranean eels, as for all those of western and 
northern Europe, the Atlantic is the one great 
breeding-ground, and that inwards, through the 
Straits of Gibraltar, pass the migrating young; 
while Dr. Grassi still inclines to his old belief that 
the deeper parts of the Mediterranean are also 
breeding-grounds. At considerable length Dr. 
Grassi discusses the other problem, and holds that 
it is by no means proved, as Dr. Schmidt would 
have it, that the Leptocephali are dwellers in the 
upper layers. He refers to the habit, which many 
species at least of the Leptocephali have, of 
burrowing in the sand or hiding under stones; he 
states that he has seen L. brevirostris itself actu- 
ally doing so; and he tells us that in captivity 
the little Leptocephali avoid the light, and retreat 
into dark corners of the aquarium. In short, he 
is unwilling to budge from his old opinion, set 
forth twenty years ago, that the Leptocephali 
come only occasionally towards the surface from 
the great depths which constitute their natural 
| home. 
The question is curiously interlinked with the 
too little-known habits of the sunfish, Orthagoris- 
cus mola. Multitudes of Leptocephali are found 
within the stomach of that fish, and would even 
seem to constitute its main, though not exclusive, 
nutriment. Sometimes, and this in itself would 
seem rather to tell against Prof. Grassi’s view, 
they are still actually living when the fish is 
2 See Dr. Schmidt's article in NATURE, August 22, 1912 ; also Dr. Johann 
Hjort’s communication to NATURE of November 24, rg10. 
