xxii APODES 60 1 



Nearly 150 recent species are known, of which some 50 are 

 deep-sea forms, occurring down to 2500 fathoms. Scanty fossil 

 remains, referable to recent genera or scarcely different from them, 

 are known from the Eocene of Europe. The Cretaceous genus 

 Urenchelys, from England and the Lebanon, is interesting as 

 representing a more generalised type, the hindmost vertebrae bear- 

 ing a pair of expanded hypural bones, showing the diphycercal 

 Eels to have been derived from Fishes with a normal caudal fin. 



The genera are numerous. The following are the principal : 

 Anguilla, Simenchelys, llyopliis, Conger, Coloconger, Congromuraena, 

 Uroconger, Jfeteroconger, Muraenesox, Nettastoma, Nettophichthys, 

 Saurenchdys, Nettenchelys, Myrus, Myropliis, Derichthys, Chilo- 

 rhinus, Muraenichthys, Liuranus, Ophiclitliys, Moringua. 



In the first four genera, small, more or less lineal rudimentary 

 scales are embedded in the skin, arranged in small groups, which 

 are placed obliquely at right angles to one another, forming a 

 curious pattern ; but these scales are so small that they escape 

 the notice of the superficial observer, hence Eels have been 

 improperly included among the Fishes forbidden as food by 

 the Mosaic prescriptions. In the other genera, including the 

 exclusively marine Conger of our coasts, scales are really absent. 



The Common Eel (Anguilla vulgaris) has a very wide dis- 

 tribution, being found over the greater part of Europe, North 

 Africa, Temperate Asia, and perhaps also North America east of 

 the Eocky Mountains, Mexico, and the West Indies. Its record 

 from Australia and New Zealand is probably due to the imperfec- 

 tion of our knowledge of the specific characters. It is not found 

 in the Black Sea nor in the rivers flowing into it, owing, no doubt, 

 to the sulphurous nature of the bottom of the sea, to which, as 

 we now know, these Fish would have to resort for breeding. 



The mode of propagation of the Eel long remained a mystery, 

 from the fact that individuals found in fresh water never 

 show ripe genital glands. The idea had been entertained of their 

 being hermaphrodite, and internal parasites had also given rise 

 to the belief in their viviparous nature. The genital glands of 

 the female were first investigated by Rathke in 1838, but it was 

 not until 1874 that those of the male were discovered by Syr.sk i, 

 and shortly after fully described by L. Jacoby, who, in his final 

 contribution to the subject, concluded that Eels need salt water 

 for the development of their organs of generation, and that this 



