- 174 - 



length is relatively inconsiderable, only ca. 13/4 mm., but on the other hand the height of 

 the body at this period becomes greatly reduced. 



If we look closer at the Table, we notice that there is a space of ca. 9— lo months 

 between the 1st Stage and the colourless young of the 5th Stage measured in March- 

 April, whereas there is only 2 — 3 months between the last and the pigmented young of 

 the 6th Stage measured in June. In the last 2 — 3 months of the metamorphosis (from 

 March— April to June) the total length is thus reduced just as much as in the first 

 ca. g — 10 months. It appears therefore, that whilst it is the height of the body 

 which is specially reduced in the first part of the time taken up by the metamorphosis, 

 it is mainly reduction in length which takes place in the last part of the period. When 

 the height of the body is almost reduced from the compressed Leptocephalus stage to its 

 final condition (as is the case in the colourless young of Stage 5), the further reduc- 

 tion induced by the still incomplete metamorphosis seems thus to affect chiefly the body- 

 length. When nothing more can be taken, from the height it must be taken from 

 the length 1 



It should be remembered here, that the biology of the young eels (or eel larvae) 

 during the later part of the metamorphosis from the 5th Stage onwards is characterised 

 first and foremost by the migration into the coasts and the fresh water. To gain their 

 goal they put forth all their energies and take no nourishments In this way the very 

 considerable reduction in the size of the body becomes comprehensible. 



The metamorphosis is completed in the summer months in Denmark (and probably 

 also everywhere in North and West Europe)^ It has thus lasted ca. 1 year, 

 during which time the fish have taken no food. 



In saying that the metamorphosis has lasted 1 year, I should state that by meta- 

 morphosis I mean the whole of the retrogressive change from Stage l (where all the 

 larval teeth are still present and the length of the postanal portion ol the body is ca. '/s 

 of the total length) to the end of Stage 6, in which the small eel young have reached 

 the smallest size they will reach. Defined in this way the period of metamorphosis 

 corresponds with the period during which the larvae do not take any nourishment. 



After the completion of the reduction in the body and therewith the end of the 

 last stage (6th) in the metamorphosis the young eels are well pigmented above and 

 the body is almost cylindrical. In the Italian specimens the average length is now ca. 61 

 mm. according to Gr.\ssi and Calandruccio (189.7, 1. c, p. 14), who even found them 

 as low as 51 mm. 3. In Danish (and most probably in all the Atlantic) specimens the 



I It is stated by Grassi and Calandruccio (1897, I.e., p. 13--14), that the colourless eel yonng ("hemi- 

 larvae" = my 5th Stage) do not feed. This has also been proved by A. C. JOHANSEN (1905, I.e., p. 8), who 

 investigated over 30 specimens from the North Sea and the Danish waters and found the alimentary canal 

 empty in all of them. 



- In the west of Europe many eel young migrate much earlier into fresh water than is the case on the 

 coasts of the north of Europe, specially Denmark. In these, the metamorphosis from the 5th— 6th Stage must 

 possibly be undergone more quickly (cf. Vaillant's description. Section II, Chap. 5, b). 



3 lu considering Grassi and Calandruccio's figures of the metamorphosis of the larval eels (I.e., 1897) 

 it should be noted, that the last figure (Fig. 6, p. 14, -see my Fig 2) compared with their .second last (Fig. 5, 

 p, 13) does not give a correct representation of the reduction in length between these two stages, the second 

 last specimen figured being of an average size (according to the Italian authors), whilst the last is the smallest 



