CLASS CEPHALOPODA: ORDER DIBRANCHIATA. 343 



account of their using their delicate shell as a boat, their ten- 

 tacles as oars, and their expanded mantle as a sail. The 

 female secretes an unchambered shell for transporting her 

 eggs, but is not united to it, though she swims backward with 

 it by enveloping it in her two broad disks and forcing water foi-- 

 ward through her breathing funnel. The male has no shell. 



The LoliginidsB are the ^^ ^^^ 



" cuttle-fish " of the Atlantic 

 coast. There are many spe- 

 cies, some furnishing the 

 thin "pen" and others the 



thick " cuttle-bone " used for J^WO bartran&i, Sqnid, Atlantic. J, 



canaries. Some varieties are the "squid" which form the 

 food of the sperm whale. 



The eight-armed cuttle-fish {Sepia octdpus) often grows to 

 a length of eight feet, with arms reaching twice that dis- 

 tance. The ten-armed {S. officinalis) is common in the 

 Mediterranean Sea. Its ink is a favorite pigment used in 

 water-color painting, under the name of sepia. Its cuttle- 

 bone is a calcareous internal shell occupying a hollow in the 

 back. The Sepiae are flesh-eaters, devouring fishes, crusta- 

 ceans, and moUusks. In turn they are the prey of the 

 porpoise and dolphin, who eat only the tender head and 

 arms, and reject the rest of the body. The shore of the sea 

 at certain places is covered with these mutilated remains.* 



ORDER TETRABRANCHIATA. 



G-eneral Characteristics. — The Tetrabranchiates (four- 

 gilled) have an external chambered shell, the partitions of 

 which are united by a tube called the " siphuncle." As the 



* These mooeters of the deep have farniBhed material for the novelist and the 

 painter. See Victor Hugo's " Toilers of the Sea," and Harper's Magazine, vol. xxi, 

 page 185. Their accoants are greatly exaggerated. — Mr. Beale in his Naturai 

 History of the sperm-whale describes a specimen of the so-called " Rock- 

 squid," not larger than his flat, but with arms expanding four feet. He grasped one 

 of its tentacles, but the cuttle-fish held to the rock with its suckers so strongly as to 

 resist all his strength. A sndden jerk exasperated the animal, which fixed its glaring 

 eyes npon its tormentor and, suddenly releasing its hold, sprang upon his naked 



