90 LOLIGO PEALII. 



muscular action, can be changed at will, producing the play of 

 color referred to in the notes on habitat. What useful purpose 

 might this change of color serve in the economy of the animal ? 



b) At one end of the body, and on the plane of one part of the surface, 



is a broad swimming-fin. At the other end of the body is the 

 large head bearing a circular group of arms. How many of the 

 latter ? Are they all alike in shape and appearance ? Is there 

 any symmetry in the arrangement of the arms or that of the 

 external parts of the body in general? 



c) On a portion of the surface of each arm are a great many suckers 



grouped in orderly arrangement. Study this arrangement. Is it 

 the same on all the arms ? 



d) Clip one of the larger suckers from an arm and study its structure. 



You will observe a stalk-like part, the peduncle, and a cup-shaped 

 portion having a thin outer rim. Within this rim is a horny ring 

 and, in the central depression of the cup, a disc-like piston forming 

 a continuation of the peduncle. It will be left to the student to 

 suggest the function of each part of the sucker. 



e) A pair of large eyes, resembling those of a vertebrate animal, are a 



conspicuous feature of the squid. They usually lack fullness in a 

 preserved specimen, partly due to the fact that the sea water, which 

 can enter the space between the cornea, and the pupil, has 

 drained out through the opening by which it had entered. Locate 

 this small opening in the space between the eye and the base of the 

 arms. Can you suggest a use in the ODtical mechanism for this 

 enclosed sea water ? 



f) A fold of tissue on the side of the head behind the eye is termed the 



olfactory organ. 



g) Push aside the arms and note, in the center of their enclosing circle, 



the mouth. Partly protruding from the mouth, or at least not far 

 down in its cavity, may be seen the tips of a dark colored horny 

 beak somewhat resembling that of a parrot. 



h) The student W 7 ill observe that the neck of the squid projects from a 

 cavity formed by an enclosing circular wall of firm, thick tissue. 

 This cavity is the mantle cavity, into which the head and neck 



