SORTATION. 



2 5 



This leaves us with the eels and the eel-like. In the eel-like the 

 skin does not extend over the gill-covers ; in the eels it does. Of 

 those in which the gill-covers are not hidden there are only 

 Ophidium, in which the ventrals are represented by a pair of filaments, 



and Fierasfer, in which the ventrals 

 are gone without any external 

 traces. Of Ophidiunt only one 

 British example is recorded, and 

 of Fiemsfer only two, so that they 

 are not likely to trouble the fisher- 

 man. Of eels there are three 

 species, each of a different genus. 

 Murcena has no pectorals ; Conger 

 and Anguilla are alike in having 



Fig. 8. CARDIFORM TEETH. 

 (Conger,) 



rctorals, but in Conger, the upper jaw is the longer, and in Anguilla 

 is shorter. The Mur&na is a rarity ; it is a rich purplish brown 

 and yellow in colour. The other two eels are common enough ; the 

 conger, much the larger and fiercer look at the " cardiform " teeth 

 in his jaw, placed so closely together as to form a cutting edge (Fig. 

 8) has always been assigned to one species, C . vulgaris, but the 

 male and female eel were long assigned to two species or more, and 

 have only of recent years been put in their right place. 



Fig. Q. HOMOCERCAL TAIL. 



The fishes that are left have well-defined tails, but it is apparent at 

 once that these tails are of two different types, the majority having 

 the lobes equal, but a by no means insignificant majority having 

 one lobe much larger than the other. In the first group the tail is 

 " homocercal," in the second it is "heterocercal." In Fig. 9 we 



Fig. 10. HETEROCERCAL TAIL. 



have a homocercal tail, and in Fig. i will be seen how this form is 

 produced by the last of the caudal vertebrae articulating with the 

 fan-shaped hypurals, which, with the neural and haemal extensions, 



c 



