20 



and tifth arms on the other. This sac eonimunicates with its mate and contains 

 the peduncle of the fourth arm which is attached with the opposite arm to the 

 lower side of the head. The peduncle of the tentacle is oval in section and is 

 very extensible so that the entire length of the tentacle varies from once and 

 a half to thrice the length of the sessile arms. The club is ovate and acute 

 and has four rows of suckers. The margins of the club bear membranes 

 somewhat widei" than those of the sessile arms and the membranes are not 

 supported by muscular buttresses but by the pedicles of the external rows of 

 suckers. The external surface of the club bears a strong, keel-like membrane 

 similar to the external membrane of the third arm. The distal portion of this 

 membrane is folded upward against the club and lacks chromatophores upon its 

 upper surface. 



While the squid is swimming the arms are pressed together so that they 

 form a flattened lance-shaped plate that is used , as a fin , for steering. The 

 sessile arms form a flattened tube which encloses the peduncles of the tentacles 

 and from which the two clubs project as the point of the fin. The edges of 

 the fin are formed by the broad external membranes of the third arms and of 

 the clubs. The squid always darts at its prey with the arms foremost and 

 just as it comes within reach , it spreads out the sessile arms Uke the rays of a 

 chrysanthemum and , by extending the peduncles of the tentacles , thrusts out 

 the clubs, seizes the prey, and then draws it back to the mouth where it is 

 grasped and held by the sessile arms. 



Each arm is composed primarily of a cylindrical column of muscle which 

 contains at its center a large nerve cord and which supports the suckers and 

 the marginal membranes of the arm. This central column is formed by a large 

 number of longitudinal mu.scle fibres which lie just inside the superficial fascia 

 surrounding the column and by numerous short transverse fibres which extend 

 from side to side and separate the longitudinal fibres into bundles. The transverse 

 fibres interweave around the large central canal for the nerve and bloodvessels. 

 One or more broad and thin sheets of longitudinal muscle fibres are attached to 

 the external surface of this column. 



The muscular ridges which support the marginal ridges or membranes of 

 the arms are formed by interlaced muscle flbi-es and ai-e attached to the outer 

 surface of the above described column by means of fibres which mingle with 

 the transverse fibres of the arm. The pedicles of the arms are attached in the 

 same way. 



The suckers are shallow suction or adhesive cups, stiffened by rings of 

 chitin-like material and attached to the arm by conical muscular stalks or pedicles. 



