BREEDING PLAICES OF THE EEL SCHMIDT 309 



the two species, however, are aj^parently not separated, but seem to 

 overlap. 



The early tiny larvse, 7-8 mm. long, of Anguilla rostrata were 

 taken in Febriiary.^^ In April the average length was abont 20-25 

 mm., in June about 30-35 mm., in July about 40 mm., and in Sep- 

 tember about 50-55 mm (cf. fig. 14). Toward the end of the year 

 the larvae have attained their full length, about 60-65 mm. ; meta- 

 morphosis takes place during the winter months, and in spring the 

 hosts of elvers move up into fresh water. We have examined samples 

 of pigmented elvers from St. Croix, West Indies (March), from the 

 Potomac at Washington (April), and from Little Kiver, Mass, 

 (May) . The average length in the two latter cases was about 57 mm. 



From the data to hand, then, we may conclude that the American 

 eel spawns earlier, that its larvae grow more rapidly (cf. fig. 14), and 

 that the full-grown larva is smaller than is the case with the Euro- 

 pean species. A result of this is that Anguilla rostrata can complete 

 its full development from egg to elver in about one year, whereas An- 

 guilla vulgaris^ as we have already seen, takes about three years. The 

 photograph, Plate 6, Figure 2, in comparison with Plate 6, Figure 3, 

 illustrates this, and shows that the I group of Anguilla rostrata in 

 June are already metamorphosed elvers, while this stage of develop- 

 ment is in the case of Anguilla vulgaris only attained by the III 

 group. Despite the fact that the two species are outwardly so alike 

 as to be hardly distinguishable, they differ to such an extent that the 

 one takes about three times as long as the other to pass through the 

 same cycle of development. 



The recognition of this difference between Anguilla rostrata and 

 Anguilla vulgaris is of decisive importance to the comprehension of 

 the life history of the two species, and the fact provides a natural 

 explanation of several points that seemed mysterious before. 



As already mentioned, an investigation of samples of eels from 

 Bermuda showed that they all belonged to the American species 

 {Anguilla rostrata) . This in itself was not surprising. But in the 

 winter of 1913-14 both the Margrethe and Bache found the waters 

 round Bermuda populated chiefly by larvae of the European eel. I 

 called attention to this point when dealing with the collections from 

 the two vessels (cf. p. 295), but was obliged to confess that it was 



" It is not easy to distiuguish the two Anguilla species in theii- early larval stages, 

 wlieii the hindmost myomeres can not yet be counted with certainty. On an average, 

 however, Anguilla vulgaris has a few preanal myomeres more than A. rostrata. In both 

 species there are a couple of black chromatophores on the embryonic fin near the tip of 

 the tail. As a rule, these are more pronounced and remain longer in A. rostrata than 

 in A. vulgaris. In the latter they are often difficult to discern and seem always to dis- 

 appear before the larva reaches a length of 20 mm. ; in A. rostrata they are sometimes 

 discernible at a length of 30-35 mm. In several larvaj the gut contained food con- 

 sisting of minute organisms, presumably CoccolithophoridiE. 

 20397—25 21 



