GENERAL FACTS ABOUT SEA FISH 13 



A fish like the bass [Labrax) presents what may be 

 regarded as the normal condition of fins in the " spiny-finned " 

 group, and the haddock (Gadus) might be taken as the type 

 of the " soft-finned " fishes, the fins being merely rays 

 inclosed in a loose fold of the skin, in which they can lie flat 

 or stand erect. There are many departures from this normal 

 form, as is particularly illustrated in the tail-fin. Normally, 

 the tail-fin consists of two equal lobes, either joined by skin, 

 and thus suggesting a fan, or else separate, and suggesting 

 rather a prong or fork. Yet the widest difl^erences may be 

 seen on comparing the tail-fin of the thresher-shark (/flopias), 

 which has an immensely long upper lobe, with that of the 

 angler-fish (Lop/iius), the tunny {Orcynus), the deal-fish 

 (Trachypterus), the sun-fish (^Orihagoriscus), and the pipe-fish 

 {^Sygnathus). The other fin which shows the most marked 

 departure from the normal rayed condition is the second 

 dorsal, which, in the salmon family, is without rays and fatty, 

 being known in that case as an " adipose " fin. The presence of 

 a second rayed dorsal distinguishes, as will be illustrated later, 

 the sand-smelt, or atherine, from the true (salmonoid) smelt. 

 The ventral fins — that is to say, those on the lower edge of the 

 body and almost beneath the head — are absent in the pipe-fishes 

 (Sygnathus) and in some other groups. Another peculiarity 

 about the dorsal fins of some fishes is their connection with 

 the sex in the breeding season. The dragonet {Callionymus), 

 already mentioned in connection with another secondary sexual 

 character, develops long filaments on the dorsal fin of the 

 mature male ; and in other forms, such as the sword-fish 

 (Xip/iias), the young fish has proportionately longer fins than 

 the adult. 



Scales may, on the whole, be regarded as a characteristic 



covering of the class of fishes, but it must not be forgotten 



that not only are they also associated with the totally 

 The Scales. ... , , 11 1 i • 



distmct class known as reptiles, but also that in some 



fishes, even on our own coasts, they are altogether absent, as 



