12 



E1NAR LEA. 



[REP. OF THE "MICHAEL SARS" NORTH 



and it seems probable that there may be about a year's 

 difference between the small prelarvae taken between 

 June 6th and 26th and the full-grown larvae caught in 

 the spring or early summer off the coasts of the British 

 Isles. If the spawning place of the eel lies to the SW of 

 the Azores and the young migrate in a north easterly 

 direction, they must require a long time to reach the 

 coasts of Europe. It is therefore not improbable that the 

 full-grown larvae are more than a year old, since they 

 are of about the same size as many other fishes at such 

 an age. In my opinion it is improbable that the small 

 prelarvae are as much as one year old. The rate of 

 growth is in nearly all cases greatest in the earliest periods 

 of the life-history of an animal. According to C. H. 

 Eigenmann, "The Egg and Development of the Conger 

 Eel" (8), five days after leaving the egg, the larvae of 

 the eel were more than 10 mm long, while embryos 

 taken out of the egg, measured 5 or 6 mm, so that during 

 the five first days the rate of growth was about 1 mm 

 per day. Although this does not refer to the eggs and 

 larvae of the common eel, we may expect to find in that 

 form a similar rapid growth, a little less or a little more. 

 Assuming that the larvae of the eel just after being hat- 

 ched grow 1 mm per day, and that it takes a year to 

 grow from the size of a prelarva (53 mm) to the size of 

 a full-grown larva (75 mm), corresponding to 0-06 mm 

 per day, we may suppose the average rate of growth of 

 prelarvae, of a size between the newly-hatched larvae and 

 those caught in June to the SW of the Azores to be 

 intermediate between 1 mm and 0-06 mm per day, that 

 is to say about 0-53 mm per day. At this rate it will 

 take 100 days for a newly-hatched larva to grow to a 

 size of 53 mm i. e. so that the prelarvae might have 

 been hatched out in February or March. Granting an 

 error of — 100 days and— 50 days 1 ) in these estimations, 

 the larvae would be between about 2 and about 6V2 

 months old, i. e. they were at the earliest hatched out 

 about the New-year and at the latest in April. 



Judging from these estimations and presuming the 

 spawning place of the eel to be not far from where the 

 youngest larvae have been found, it is unreasonable to 

 suppose that the migrating silver-eels caught in Danish 

 and Swedish waters during the autumn, and in the English 

 Channel during December (according to Cligny's commu- 

 nications in the Comptes Rendus (5)) could possibly spawn 

 in the neighbourhood of the Azores in the course of the 

 first winter after emigration. Their spawning migrations 

 must cover vast distances, and even at the rate of 15 

 km per day, they should need months to reach the 

 Azores. 



2. Leptocephalus Synaphobranchi pinnati. 



We find eleven specimens of this species in the 

 material, of which six do not exceed 60 mm in length, 

 whereas the other five must be characterized as full-grown 

 or metamorphosing larvae. The segments, 144 to 157 in 

 number, have a peculiar shape like two arches meeting 

 at the lateral line and forming quite a sharp angle, the 

 point directed forward. The segments are very transparent, 

 except along the lateral line, where they are opaque (at 

 any rate in the preserved specimens), giving these lepto- 

 cephali a characteristic appearance with quite a light lateral 

 stripe. (See pi. II). 



For a detailed description of the full-grown larvae I 

 refer to Schmidt's papers, but will describe the six smallest 



Fig. 5. Head of larva no. 1. 10 /i. 



specimens, which represent a developmental stage, hitherto 

 unknown in this species. 



The smallest and youngest specimen (no. 1) measures 

 43 mm from point of snout to tip of tail, and has 104 

 preanal and 46 postanal myomeres, 150 in all. I could 

 count 10 teeth in each half of the upper jaw, and 1 1 or 

 12 in each half of the lower jaw. The foremost tooth 

 of the upper jaw is large and curved and directed forward; 

 farther back we find first one big, strong tooth, then after 

 an interspace eight rather small teeth. In the lower jaw 

 there is also foremost a curved tooth, directed forward, 

 followed by five strong teeth and five smaller ones 

 (see fig. 5). 



The nostrils are not separated; we can see nothing 

 but a triangular groove, almost intermediate between the 

 point of the snout and the lens of the telescopic eye. 



The pectoral fin is fan-shaped, and has a striped 

 structure, but no true spines. In the margin of the posterior 

 portions of the embryonal dorsal and ventral fins, the first 

 traces of interspinous elements can be seen. They arise 

 out of the embryonic fin without any connection with the 

 body, just as described by Schmidt in Leptocephalus 

 hyoproroides (later renamed L. thorianus). 



In the caudal fin the rays are present, H, having 

 eight, and H 2 nine. These rays are separated from the 

 posterior interspinous elements of the anal and dorsal fins 



1 ) The probability of a large positive error is greater than of a negative one, for the latter cannot exceed 100 days. 



