Cephalopoda. 139 



head and a distinct neck. At the tail end are two triangu- 

 lar fins which together present the appearance of a dia- 

 mond-shaped arrow point. Seen from below the body is 

 conical or fusiform, ending in a distinct point behind, the 

 tail fin covering about one third of the body. The fins are 

 attached at the sides of the dorsal part of the hinder part 

 of the body, and can be wrapped more or less around the 

 tapering posterior end. The common kinds of squids sel- 

 dom attain a length of a foot. 



The Head. From the front of the head project five 

 pairs of arms, arranged in a circle around the mouth. 

 Four pairs of these arms are short, and taper to a point. 

 One pair are much longer, being nearly as long as the body, 

 and are enlarged near the ends. On the inner surfaces of 

 the short arms, and on one side of the club-shaped end of 

 the long arms, are rows of suckers. These are button- 

 shaped or saucer-shaped bodies, attached to the arms by 

 stalks. The outer surface is hollow, and when applied to 

 any surface the center can be retracted by the muscular 

 stem by which it is attached, thus making a strong hold- 

 fast. The long arms are sometimes called the "grasping 

 arms." 



On the sides of the head are the two large eyes, the 

 most highly developed eyes among the invertebrates. 



The Mantle. There is an opening all around the neck 

 where it projects from the mantle cavity. The whole 

 external envelope of the body is the mantle, inside which 

 is the conical body, with a space extending nearly all around 

 it except along the dorsal line, where the outside of the 

 body mass is attached to the inside of the mantle. The 

 mantle is muscular and very powerful. 



The Pen. The squid has no external shell, and the 

 only representative of one is a horny structure, somewhat 



