296 



COLLEGE ZOOLOGY 



Tentacle 



FunneH 



0,^1 



Gas chamber 



' — Siphuncle 

 Chamber partition 



Figure 185. Chambered (pearly) nautilus with shell cut away to the midline to show the 

 animal and the many gas filled chambers in which it lived at successive stages in its growth. 

 The siphuncle is a limy tube that encloses a cord of living tissue which extends from the last 

 chamber to the first one formed. It lives in the south Pacific Ocean. Natural size up to 10 

 inches in diameter. 



The chambered nautilus (Fig. 185) was 

 immortalized by Oliver Wendell Holmes in 

 his great poem, "The Chambered Nautilus," 

 in which he called it "the ship of pearl." It 

 has a shell that is coiled like a watch spring 

 and is divided by cross walls into a series of 

 compartments. A new and larger chamber is 

 built when the old compartment is out- 

 grown, and a new wall is secreted behind it. 

 The head bears 60 to 90 tentacles without 

 suckers. 



Octopuses (devilfishes) (Fig. 186) live in 

 dark crevices and in coral reefs. Most of 

 them are not large enough to harm a hu- 

 man being, but the giant octopus of the 

 Pacific reaches a diameter of about 30 feet 



and can be dangerous. These are feared by 

 pearl divers. 



Bivalve mollusks 



Bivalves (Fig. 172) may live in fresh 

 water or in the sea. More than 500 species 

 of fresh-water clams live in the United 

 States and many species of oysters have 

 also been described. Adult oysters are unable 

 to move about, being attached by the left 

 valve to some solid object. Oysters feed in 

 much the way fresh-water clams do. A single 

 oyster may deposit approximately a half 

 billion eggs in one season; these develop in 



