EINAR LEA. 



[REP. OF THE "MICHAEL SARS" NORTH 



II. Descriptions. 



/. Leptocephalus Anguillae vulgaris. 1 ) 



(L. brevirostris). 



The larvae of the common eel caught during the cruise 

 number 44, and they may according to their degree of 

 development be separated into three divisions: 1) small 

 larvae, not yet having attained their full larval develop- 

 ment, 2) full-grown larvae, not yet showing any sign of 

 retrogressive metamorphosis, and 3) larvae showing retro- 

 gressive metamorphosis. 



mm. 







40 









45 







50 



000000000 



"Prelarvae" 



55 



00000000 



60 









65 









70 



000000000 



Full-grown and meta- 



75 



00000000 



morphosing larvae. 



80 









The above diagram shows how the larvae group 

 themselves according to size, (each circle representing 

 one larva) into two groups: one in which the individuals 

 are mostly 50 or 55 mm, and another in which the indi- 

 viduals are mostly 70 or 75 mm long. The latter group 

 includes full-grown and metamorphosing larvae of nearly 

 the same size and character as those known from Schmidt's 

 investigations in the Atlantic. 



In the following table the larvae are arranged accord- 

 ing to size, no. 1 being the smallest, no. 44 the largest. 

 The last column indicates the category to which the 

 larvae have been referred, full-grown being identical with 

 Schmidt's first stage, and "metamorphosing" with Schmidt's 

 second stage. 



The table brings out the following differences be- 

 tween the "prelarvae" and the full-grown specimens of 

 stage I: 1) They are much smaller, the difference in length 

 being on an average 20 mm, and the largest prelarva 



is 6 mm shorter than the smallest of the full-grown lar- 

 vae; 2) the head in the prelarvae is relatively larger than 

 in the full-grown larvae, viz. 8 or 9 per cent of the 

 length in the former, and only 6 or 7 per cent in the 

 latter; 3) the eye is also relatively a little larger, the 

 difference, however, being so slight as to be noticeable 



Fig. I. Head of the smallest eel-larva (no. 1). 10 /i. 



Fig. 2. Head of eel-larva no. 21. 10 /i. 



only when we compare the averages (24-1 per cent in 

 the former and 22-7 per cent in the latter). As for the 

 remaining characters the small larvae are practically like 

 the big ones of stage I. 



To these differences we may add the following. The 

 heads of the small larvae are rather angular, the end of 

 the snout often an almost straight line. The teeth give 

 the impression of being relatively larger, but then there 



J ) In "Nature" for November 24, 1910, Dr. Johan Hjort has accounted for the catches of eel-larvae made during the "Michael 

 Sars" expedition. The account given here is an extension of the preliminary description. 



