CEPHALOPODS. 



329 



occur in all seas. Variations in colour, the relative length of the arms, the size 

 of the suckers, and the character of the hectocotylised or modified arm of the male, 

 are among the distinguishing features of the species. Although we usually speak 

 of the octopods as shell-less or naked molluscs, an indication of an internal shell 

 is present, in the form of two short styles, embedded in the tissues of the mantle. 

 These molluscs are solitary creatures when adult, but they are said to herd together 



COMMON OCTOPUS. 



in small companies when young. They live in the fissures of rocks, or hide away 

 beneath great boulders. When they walk or creep, they elevate the sack-like 

 body above the head, and progress slowly upon the extremities of the arms, which 

 are a little curved near the tip. They can creep in any direction, but they prefer 

 a side-way movement. On the contrary, if their progress in walking is com- 

 paratively slow, this is compensated by the rapidity of their movements when 

 swimming. Body foremost, with the arms stretched beyond the head, they dart 



