A SQUID 123 
CEPHALOPODA 
A DIBRANCHIATE CEPHALOPOD. A SQUID (Loligo pealii) 
The squid is a very common marine animal. It is social 
in its habits and swims about in large schools in search 
of its food, which consists of crustaceans, small fishes, etc. 
When alarmed by the presence of its natural enemies, which 
are many kinds of fishes, it clouds and darkens the water 
by ejecting into it an ink-like fluid. The fresh animals are 
studied with greater profit than those which have been pre- 
served in alcohol, as this changes the nature and appearance 
of many of the organs; if they must be preserved, formalin 
should be used. 
External anatomy. Observe the cylindrical, bilaterally sym- 
metrical body; at one end is a pair of broad fins, and at the 
other, the movable head bearing ten arms, two of which are 
much longer than the others. The mouth is at the base of and 
surrounded by the arms, and the brown horny beak may usually 
be seen protruding partly from it. The large eyes are on the 
sides of the head at the base of the arms. Lach is covered by 
a cornea, which is pierced by a small hole between the eye and 
the base of the arms, so that sea water is admitted freely 
into the space between the cornea and the pupil, and may 
take the place of the aqueous humor of the vertebrate eye. 
A transverse fold on the side of the head between the eye 
and the body is the olfactory organ. Observe the pigment 
spots or chromatophores which are distributed over the body; 
they are constantly changing in shape and size during life, 
causing corresponding changes in the color and appearance of 
the animal. 
