CEPHALOPODA 



A DffiRANCHIATE CEPHALOPOD. A SQUID (Lo/igo pealii) 



A SQUID 123 



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. Each 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. 



