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Part III. — Eighth Annual Report 
only propagate in the sea, or in brackish water, where the males are only 
found. The females descend from inland waters to the sea in autumn, 
and the young (female) eels ascend from the sea in spring. With the 
females are sometimes found specimens having the snout broader and of 
great size — sometimes weighing 5 or 6 kilogrammes. The reproductive 
organ in these consists of modified ovaries, that have undergone fatty 
degeneration, the ova being completely absent ; they are sterile females 
which do not descend to the sea, like those sexually developed which 
descend in autumn. Professor Vaillant states that when the eels reach 
the sea the reproductive organs are imperfectly developed ; the ova are 
not mature or ready for fertilisation. They are contained within the 
organ, they are all of the same size, destitute of vitelline membrane, 
and have never been found as in other fishes when mature, lying free in 
the abdominal cavity. Similarly, the testes show the mother cells, but 
no sperms. What becomes of the eels when they reach the sea is a 
mystery; none large or small have been obtained, and Dr Jacoby's special 
researches on this subject at Commachio were fruitless. The eel fishermen 
in France believe they perish after reproduction j but this is very 
improbable. 
Some interesting facts in regard to the eel have been recently obtained. 
At the beginning of May 1890, it was found at Howietoun that the 
water-supply from Loch Coulter had been interfered with on ten successive 
nights. On each morning a number of eels were discovered in the sluice, 
where the water is ten feet deep. Thirty females were obtained, and one 
of these, 32 inches in length, and weighing about 2 lbs. was sent in by 
Sir James Maitland, Bart. Each ovary was about 12 inches long in situ, 
and about 30 inches long when the frills or plications were measured. 
Microscopic sections were made, which showed that the ova were in 
various stages of development, some of them, 0*25 mm. in diameter, 
being nearly ripe. Mr Ramsay Smith made a calculation of the number 
of eggs present in the two ovaries, and found that these were approxi- 
mately 10,077,000. Seelcy,* gives the number as several millions ; and 
Syrski,t who has made an elaborate study of the reproductive organs 
of the eel, calculated that the ovaries contained 5,000,000. The largest 
ova obtained by Syrski had a diameter of one-fourth to one-fifth of a 
millimetra Seeley states that in August their diameter is 0'09 mm.; 
in September 0*10 mm.; in October, 0*16 mm.; and in November 0*23 
mm. The diameter of the larger ova in the Howietoun eel was, it will 
be seen, greater. Eels have been found in December and January on the 
Prussian coast with the ova having a diameter of only 0*03 to 0*09 mm. 
In the eels found at Howietoun many of the ova were very nearly 
mature ; this was apparent not merely from their size, but from their 
microscopic appearance. Many were, however, much less advanced in 
development. The sections showed very well the formation of the 
ovarian leaflets, and the progressive stages of the ova. 
There can be no doubt that these eels when caught were migrating to 
the sea, and from the condition of the ovaries it is obvious that the 
migration was for the purpose of reproduction. The interest relates to 
the period of migration. The general seaward migration of female ftwlfl 
approaching maturity takes place in autumn. Two explanations may be 
offered; (1) that these eels had by some means been prevented from 
migrating at the usual time — not a very satisfactory explanation ; (2) that 
the eels from Loch Coulter begin to migrate at the beginning of summer. 
It is known that the commencement of the migrating movement varies 
* Fresh-water Fishes of Europe, p. 378, 1886. 
t Boll, della Soc. Adricttim di Scienze naturali in Trieste, No. I. Trieste 1875. 
