198 MADRAS FISHERIES BULLETIN VOL. XIV, 



controls the muscles working the sucker's piston, in a state of 

 tension. The mouth, situated in the centre of the circlet of arms, 

 is armed with a horny parrot-like beak, in large species so powerful 

 as to be capable of rending its prey. 



The class is divided into two sections according as the number 

 of gills is two or four. Those characterized by the latter number 

 were predominant in former geological times, but to-day the Pearly 

 Nautilus is the only existing form with four gills. The two-gilled 

 section is in turn classed, according as the arms are eight or ten, 

 into the Octopoda and the Decapoda. The common Octopus and 

 the Paper Nautilus {Argonauta) are types of the former; the cuttle- 

 fishes, squids (or calamaries), and the curious little Spirula, are 

 the best known representatives of the other. 



The Octopoda have neither internal nor external shell, with the 

 partial exception of the Paper Nautilus where the female forms an 

 extremely fragile and delicate transparent shell in which she 

 brings forth and shelters her eggs. Some attain a large size and 

 mythological stories tell of huge individuals that have seized men 

 from boats. In our Indian seas the largest I have seen, Herdman's 

 Octopus {Polypus herdmani), had a body less than the size of the 

 fist, with arms about 2/^ feet long when fully extended. The 

 Octopus is by far the most intelligent of the mollusca, indeed it 

 seems an absurdity to class it with snails, chanks, oysters and 

 clams; in one sense the name of Devilfish sometimes given to it in 

 England, seems justified. If several Octopus be watched in capti- 

 vity and if they are at home in their surroundings, the cleverness of 

 the creatures in stalking their prey and their cruel rapacity in tear- 

 ing the victim into pieces when caught, are uncanny and devilish. 

 I have watched an Octopus on the prowl sliding stealthily over the 

 bottom with all the skill of a high intelligence ; every bit of cover 

 is made use of and even the colour of the bottom is imitated for 

 concealment. Passing over yellowish sand the dark body tints of 

 the Octopus fade away and there is nothing but a slight movement 

 to betray its presence. Anon it crawls over a mass of brown 

 weed — dark tints come back in a flash and once more the animal 

 is indistinguishable from its background. This ability to make 

 lightning changes in its colour disguises is due to the colouring 

 matter in its skin being in little sacs controlled by muscles. If the 

 muscles contract the pigment spots grow and expand, giving dark 

 tints to the body ; if they relax, the spots close to pin points 



