52 NATURE 

Atlantic our eels did breed, we had to find far younger 
stages, for a larva so large as 34 mm. might well be 
imagined to have moved a great distance from the spot 
where it came into the world. Nor was it enough to 
find a few isolated specimens of the youngest stages ; a 
spot which could be declared to be the site where the 

Fic. 2.—Sizes of eel larve (Ang: ‘//a vulgar7s) caught in a single haul 
of two hours’ duration at Vana Station 871 (lat. 27° 15’ N., long. 
61° 35’ W.) in the western Atlantic, June 27, 1920, depth about 50 
metres. About 800 specimens of O-group and 1 of I-group are shown. 
A II-group specimen, length 74 mm., from the eastern Atlantic, is 
shown for comparison. Reduced to about one-quarter (see the centi- 
metre-scale). 
great hosts of eels from the European continent assemble 
for their spawning must necessarily yield earliest stages 
of the offspring in great numbers. 
The task before us, then, was to chart the distribution 
of the various developmental stages of eel-larve, from 
the oldest, about 74 cm. long—which we knew from 
previous investigations were to be found off the coasts 
of Western Europe and in the Mediterranean—to the 
earliest tiny stages which no one as yet had ever seen. 
If we could ascertain where, and at what seasons, these 
tiny larvee were found, then we should at the same time 
have discovered where and when the eels spawn. Once 
it was known where the various sizes (age-groups) of 
growing larve occurred, it would be possible to form an 
idea as to the extent and duration of the migrations of 
the eel-fry from the breeding grounds to the fresh 
waters of Europe. 
These years of research have been rich in excitement 
and suspense; disappointment alternating with en- 
couraging discoveries, and periods of rapid progress 
with others during which the solution of the problem 
seemed wrapped in deeper darkness than ever. One is 
tempted to describe the investigations in their chrono- 
logical sequence, from first to last, in order to show how 
by slow degrees, advancing step by step, we came to see 
NO, 2776, VOL. 111] 


[JANUARY 13, 1923 
great parts of the life-history of the eel emerge from the 
darkness that surrounded it. The question of space, 
however, precludes this. We must content ourselves 
with setting forth the facts as theysnow appear, after 
eighteen years of work, and seeing what conclusions 
may be drawn from them. 
The chart Fig. 1 gives us the main sum of these many 
years’ investigations into the distribution of the eel larvee. 
This may be briefly stated as follows : The larvee of our 
European eel (Anguilla vulgaris) are found distributed 
across the whole of the Atlantic Ocean from off the 
coasts of Europe to those of the United States. They 
increase in number, but decrease in size, as we pass 
from the European side towards America. The curves 
on the chart show that the spawning grounds comprise 
a restricted area in the western Atlantic, north-east and 
north of the West Indies, between 65° and 48° long., 
for here—and here only—are the youngest, newly 
hatched larvee found. The eel spawns at the close of 
the winter and during spring. In April the larve had 
an average length of 12-13 mm., in June 25, and in 
October 35-40 mm. During their first summer the 
larve are found only in the western Atlantic. Enormous 
quantities of these first-year larve (the O-group, as we 
call them) are found at this season west of 50° W. long. 
In June 1920, when we were working there with the 
schooner Dana, it was impossible to draw a net through 
the upper water layers without bringing them up in 
quantities, and we often took several hundred speci- 
mens at one haul, as shown in the illustration Fig. 2. 

Fic. 3-—European eel (Anguilla vulgaris); western Atlantic (west of 50° 
long. W.), Dana Stations 935-948, April 1921 ; C-group and 3 specimens 
of I-group. 
We are therefore excellently acquainted with the sizes 
and growth of the O-group larve. In June 1920 the 
four or five thousand specimens taken varied from 
7 to 37 mm. in length, with an average of 25 mm. 
In the course of the autumn and winter, the great 
bulk of the first-year larve (the O-group) disappears 
from the spawning grounds in the western Atlantic, but 

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