2G0 



THE MECHANICAL FUNCTIONS. 



roiis suckers all along their inner sides. Each 

 of these suckers, as shown separately in Fig. 

 122, is usually supported on a narrow neck, or 

 pedicle, and strengthened at its circumference 

 by a ring of cartilage. Their internal mechan- 

 ism is more artificial than the simple construc- 



tion already described (p. 137): for when the 

 surface of the disk is fully expanded, as shown 

 in Fig. 123* b, we find that it is formed of a 

 great number of long slender pieces, resembling- 

 teeth closely set together, and extending from 

 the inijer margin of the cartilaginous ring, in 

 the form of converging radii, to within a short 

 distance of the centre, where they leave a circular 

 aperture. In the flattened state of the suckei\ 

 this aperture is filled by the projecting part of a 

 softer substance, which forms an interior portion, 

 capable of being detached from the fiat circle of 

 teeth, when the sucker is in action, and of 

 leaving an intervening cavity. The form of this 

 cavity is exhibited in Fig. c, which represents a 

 perpendicular section of the whole organ, and 

 where the central portion, or principal mass of 

 the sucker is drawn away from the circular disk, 



