18 
the whole caudal fin is stretched out on rays only. The end of 
the notochord turns up at an angle at the root of the fin, so as to 
point upwards. This kind of tail is found in most of the recent 
fishes, sometimes simply fan-shaped, as in the Sticklebacks ; 
sometimes more or less forked, as in Perch and Herrings. See 
Figs. 7 and 8. 
Now a very notable thing is this; that in the development of a 
fish from the egg, it has first a simple membranous fin, very like 
that of a tadpole; afterwards it becomes (in some cases at least) 
distinctly heterocercal, like the old-fashioned types of fish, before it 
finally assumes the homocercal form. For example, the common 
Stickleback, shortly after hatching, has a tail like Fig. 6. The 
notochord occupies the upper part, and the fin-rays are all on the 
lower side. As the fish grows, the notochord turus up more and 
more, and the end part dwindles away; so that in the adult 
Stickleback the upper half of the tail seems to match the lower, 
although nearly all the rays really spring from the lower side of 
the spinal axis. 
Besides this cauda/ fin, most fishes have an ana/ fin below, on 
the foremost part of the tail; and the dorsal fin of the back often 
extends along the tail, sometimes joining the caudal. In the 
Flat-fishes, such as soles and plaice, the vital organs occupy a very 
small part of the animal; the rest is all tail, with its continuation 
in the high ridge of the back. In these flat-fishes the roe extends 
backward far into the tail. 
The bony skeleton of a fish’s tail consists of a series of vertebre 
along the notochord; each vertebra carrying a neural arch above, 
to protect the nervous cord, and a hemal arch below, covering the 
great blood-vessels. Both these arches are often prolonged into 
spincs at top and bottom; as is well seen in the Flat-fishes. 
Among the curiosities of fish-tails are the prehensile tails of Pipe- 
fishes and Sea-horses, by which they anchor themselves among 
seaweed. Also the strange whip-like tails of Skates. rather 
suggestive of mammalian tails than any other class. In early life, 
however, the Skate’s tail is of the ordinary tapering form. 
Above the Fishes come the Amphibia, including the Efts, Frogs, 
and Toads. All these in their early stages have tails such as 
already described in the tadpole. The efts keep this primitive 
tapering tail all their life, with neural and hemal arches as in 
Fishes. The fin reaches round the back as far as the neck; but 
never acquires any fin-rays, or specialized tip. When the animal 
takes to the land, the fin disappears, being no longer needed. 
In the frogs and toads the whole tail is gradually absorbed. 
The white corpuscles of the blood carry it back into the body 
particle by particle, thus nourishing the tadpole during its great 
