MARINE MOLLUSCS 



253 



seldom exceeds four or five inches in length, and, like the Calamary, 

 is used largely as a bait by fishermen. 



Another family the Sepiadte contains the Cuttlefish (Sepia 

 officinalis), the 'bone' of which is such a common object on the 

 beach. This latter is a broad, curved plate of carbonate of lime, 

 made up of a number of regular layers, and having a cavity hollowed 

 out at the posterior end. It is exceedingly light and porous in struc- 

 ture, and at one time was used largely as an antacid as well as a 

 dentifrice. It is also proportionately large, being both as long and 

 as broad as the body of the animal. 



FIG. 186. Sepia officinalis AND ITS 'BONE' 



Cuttlefishes live principally in the shallow water close to shore, 

 where they swim backwards by the sudden propulsion of water 

 from their siphons ; and their eggs, which look like clusters of black 

 grapes, are frequently thrown up on the beach, generally attached 

 to the stems and fronds of sea weeds. 



As a rule the cephalopods swim slowly by the aid of their fins 

 or by a rhythmic contraction by which water is expelled from their 

 siphons, but when in danger the muscular contraction is so violent 

 that they dart through the water with great speed, and even leap 

 into the air to avoid their enemies. But they have another and 

 much more remarkable way of escaping from their foes : They 

 possess a gland, the duct of which opens into the base of the funnel 

 or siphon, that prepares an inky fluid ; and when the animal is 



