168 CLASS-BOOK OF ZOOLOGY. 



principally in the Lagunes of Venice, where its flesh is 

 sold as food, and its coloring substance as an article of 

 paint ; while the large bony plate of its back serves as 

 a polishing instrument, and is used also in medicine, (os 

 sepias of the druggist.) 



§ 732. The Nautilus, (Nautilus Pompilius,) which has 

 a reddish-brown body, about five inches in length and 

 three inches thick, with arms like the Cuttlefish, in- 

 habits a round whitish shell, with yellow and red stripes. 

 The shell, which has a large opening, is lined inside 

 with mother-of-pearl, and divided into chambers, in the 

 anterior of which the animal lives, making itself heavier 

 or lighter at pleasure, by pumping water into or out of 

 the other chambers. 



QUESTIONS ON SECT. XLHI. 



719. In what respect are Univalve Shells more perfect than Bi- 

 valves ? 



720. What do you know of the Cowry? 



721. What is its value ? 



722. Describe it. 



723. What do you know of the Whelk and the Harp? 



724. What do you know of the eggs of the Whelk? 



725. Of what shells does the genus Periwinkle consist? 



726. Describe the Cuttlefish. 



727. What do you know of their arms? 



728. What do you know of their blackish-brown fluid? 



729. Of what use are Cuttlefish ? 



730. Where are they found, and what is their size? 



731. What is the size and use of the Common Cuttlefish? 



732. Describe the Nautilus. 



SECTION XLIV. 



Ath Order — Prickly Worms : (EcJiinodermala, Cuvier.) 



§ 733. The Prickly Worms have a cartilaginous body, 

 in some cases with a calcareous crust, and are covered 

 with prickles ; as the Sea Hedge-hog, the Sea-star, etc. 



§ 734. The Sea Hedge-hog (Echinus) has a round or 



