68 
Tank No. 10. 
Dog-fish and Rays belong. Those in the Aquarium are chiefly Bottom- 
fishes, which display only very little of their life. Let us turn our 
attention first of all to the Sharks. 
The word "Shark” will cause the reader to think at once of those 
gigantic robbers of the ocean, which have become the terror of the sailors. 
He will therefore be a little astonished to find the Sharks of the Aqua¬ 
rium scarcely a yard in length, and will probably look upon them as 
either young Sharks or not as genuine ones. We would therefore remark 
that amongst the many forms of Sharks there are small ones which are 
however "true Sharks”, as both they and the more common Dog-fish 
agree in their characteristics with the larger species. A comparison of 
the Rock Dog-fish (Fig. 117, tank No. 10), with the Bass (Fig. 118), a 
bony fish, will quickly reveal these essential features. 
The Bass is covered over its whole body with silvery fish-scales, 
has its mouth at the anterior extremity, two large moveable gill-covers, 
staring eyes not provided with lids, and nasal apertures distinct from the 
mouth. The body of the Shark on the other hand is not covered with scales, 
but with bony spines, which cause the skin to feel rough. The mouth 
is on the under side of the head in the form of a crescent-shaped slit 
from side to side, and the neck has five or more gill-slits on each side, 
but no gill-cover. The eyes are provided with moveable eye-lids, the 
nostrils communicate with the mouth, forming a "hare-lip”, a condition 
passed through by the embryos of all higher Vertebrates. These external 
characteristics alone would distinguish the Sharks from the bony fishes, 
but there are besides many differences of internal structure. The skeleton 
of the Shark, Ray, or Dog-fish, is all gristle, there being no bone ex¬ 
cept in the spines of the skin; where this bends over the jaws, they 
are enlarged to form the teeth. The anatomy in general is less advanced 
in specialization than that of bony fishes. The commonest genus is the 
Spotted Dog-fish, Scyllium, of which two species exist in all European 
seas, S. catulus, the Rock Dog-fish, or Bounce, as it is frequently called, 
and S. canicula, the Little Dog-fish or Morgay. The first is about a 
yard, the latter about two feet in length, so that they both belong to 
the smaller forms. They are lazy fishes, which seek their prey usually 
at night-time, and lie hidden in the corners of the tank during the day. 
They are fed on dead fish, which in day-light they find chiefly by their 
sense of smell, as their eyes are then quite useless; they search about 
close to the bottom of the tank, and only notice their food when they 
touch it with their snout. 
The female lays its eggs singly on branches of coral (e. g. Tank 10 on 
the right) or attaches them to bushes or rocks. They are contained in rect¬ 
angular, leathery capsules known as Mermaid's or Sailor s purses, semitrans¬ 
parent and white when first laid, but afterwards becoming yellowish brown. 
The corners of the case are provided with long horny filaments, with 
which the fish attaches the eggs to the corals or other objects by 
swimming round and round them as the egg is being pushed out of the 
body. Thus the eggs are prevented from being covered by the mud, which 
is one of the many enemies of the embryo. The development of the embryo 
can be very well observed owing to the transparency of the case; this 
