ALLIES OF THE PELECYPODA : MOLLUSCA 191 



Another and still more effective means of escaping from 

 the attack of a superior enemy is employed by the squid when 

 driven to its last resource. It has in its body-cavity a sac 

 which secretes a black, inky fluid. A tube from the ink-sac 

 passes to the siphon, and in the moment of need the sac and 

 the muscular mantle contract and force the black, confusing 

 fluid into the water. The squid then has a chance to escape. 



The Chambered 

 Nautilus. Almost 

 the sole represent- 

 ative of a once 

 numerous race 

 living in the 

 depths of the sea, 

 the chambered 

 or pearly nautilus 

 (Nau'tilus pom- 

 pil'ius, Fig. 97) 

 now has a restrict- 

 ed distribution in 

 the vicinity of cer- 

 tain South Pacific 

 islands, such as 

 New Guinea and 

 the Philippines. Nautilus lives on the bottom, usually in 

 water from one hundred to seven hundred meters deep (three 

 hundred and twenty-five to twenty-three hundred feet). 



The shell of Nautilus is divided into compartments by 

 cross-partitions. Each of these compartments represents a 

 space in which the animal lived at successive stages in its 

 growth. The chambers of the entire series are filled with air 

 and are connected by a slender tube called the siphuncle^ 

 borne in a thin-walled, calcareous tube (Fig. 97, 11 ). The 

 siphuncle is a part of the animal's body proper. A mantle 



FIG. 97. Nautilus. Reduced. (After Ludwig) 



1, mantle ; 2, dorsal fold of mantle ; 3, tentacles ; 4, head- 

 fold ; 5, eye ; 6, siphon ; 7, position of nidamental 

 gland ; 8, shell-muscle ; 9, living chamber ; 10, parti- 

 tions between chambers; 11, siphuncle with tube 



(From Hertwig-Kingsley's General Zoology) 



