21 



The size and symmetry (»f tlie suckers depend ujion their age and position. The 

 arms grow continually and new suckers are added from time to time at the 

 more rapidly growing apex. Hence , except on the tentacles , the largest suckers 

 lie at the base (_>f the arm and the smallest at the apex. At the base of the 

 club of the tentacle, there are a few suckers that are smaller than those nearer 

 the middle of the club. Few , if any , of the suckers are symmetrical and the 

 majority are very unsj'mmetrical. Those of the central rows of the club are 

 the largest and most symmetrical while those of the lateral rows and of the 

 sessile arms are very unsymmetrical. The side of the sucker farther from the 

 center of the arm is enlarged and the opposite side is correspondingly reduced 

 so that the most unsymmetrical suckers become little more than complex hooks. 

 This arrangement of the suckers suggests that the t)bliquity of the strains to 

 which they are subjected when in use causes the asymmetry of the suckers. 



The pedicle of the sucker (Plate I . Fig. o) projects inward from the inner 

 surface of the arm. It is formed by a large number of longitudinal muscle 

 fibres bound together by a few transverse fibres. The majority of the longitudinal 

 fibres arise h'om the outer surface of the arm and bend around it beneath the 

 marginal membranes of the arm to the inner surface where they join other 

 fibres arising from the middle of the inner surface of the arm. The pedicle 

 thus formed contains the nerve and blood vessels of the sucker and terminates 

 in a strong fascia which lines the base of the cup of the sucker, and from 

 which the muscle fibres of the sucker arise. This cup consists of a very thick 

 muscular base with a deep central depression and of a low rim supported by. a 

 thick toothed ring of chitin-like material. The center of the base of the cup is 

 formed solely by the top of the pedicle vv^hich is called the "piston" because it 

 acts as the piston of a pump whenever the arm is withdrawn after the sucker 

 has been pressed against a surface. The muscle fibres which form the base of 

 the sucker arise from the fascia that lines the cup and that is attached to the 

 pedicle. The fibres pass obliquely downward and outward to the outer surface 

 of the cup and end in a fascia which supports the sides of the suckei'. The 

 outer ends of the fibres are separated by a few small bundles of circular 

 (sphincter) muscle fibres. The side of the cup is formed chiefly of three muscles. 

 The largest of these is a strong sphincter which forms its lower part. The 

 other two muscles arise from the external superficial fascia of the sucker and 

 one is inserted upon the lower half of the ring: the other upon its upper half. 



The ring is a broad band which is strengthened by a strong external ridge 

 that separates the two muscles just mentioned. The free edge of the ring of 

 the symmetrical suckers has about thirty large teeth separated by as many 



