50 
Tanks No. 19 and 24. 
A very near ally of Octopus is Eledone moschata, the Musk-octopus 
(Tank 24}j much smaller and with only one row of suckers on each 
arm. They are very shy and try to hide themselves from view. When 
taken out of the water they give out a strong odour of musk. As they 
are, frequent in occurrence they are often brought to market, but are 
generally only eaten by the common people. 
One of the most interesting and most important of the Cephalopods 
is the Sepia or Cuttlefish (Sepia officinalis, Fig. 80, Tank 19). Their 
Fig. 80. Sepia officinalis, nat. size. Tank 19. 
body is oval, somewhat flattened, and with a membranous fin running 
down both sides. Beneath the dorsal skin is the "cuttle-bone”, found often 
on the English coast and given to captive canaries to sharpen their beaks. 
The eight arms are much shorter than those of the Octopus and are 
generally carried closely applied together; between them is hidden an¬ 
other much longer pair of arms which can be shot out to catch crabs or fish. 
The most noticeable characters in Sepia are the excretion of an 
inky fluid and the change of colouring in the skin. Both of these they 
have in common with the other Cephalopods, but they make more frequent 
use of them. The sepia used by artists is the product of a gland, the 
so-called "ink-sack”, the contents of which can be squirted out through 
the funnel; a small quantity is enough to suddenly envelope the animal 
in a black cloud, which hides it from its pursuer. The ink is extracted, 
dried and brought to market; even that of fossil forms can still be used. 
— The wonderful play of colours on the living animal is due to large 
cells (Chromatophores) which are situated in the skin and are filled with 
finely divided dark colouring matter; as these cells contract (become glo¬ 
bular) and expand (become flat), a continuous change of colours takes 
place; stripes, spots and markings make their appearance and disappear 
according as the animal is at rest or is irritated. The Cuttlefish have 
complete control over this change of colours; this is seen from the 
protective colouring, which they assume when they lie on the sand or 
on dark rocky ground; in either case they can hardly be distinguished. 
— The males court the females with great ardour and in their excited 
state produce most brilliant colours over their body. The female lays large, 
black, pear-shaped eggs and fixes them singly to corals and algae, usually 
closely together, so that they form large grape-like clusters (often visible 
in tank 19). As soon as the young are hatched they shew their pro¬ 
ficiency in changing their colouring and emitting the sepia. 
