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GENERAL ZOOLOGY 



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 siphun- 

 cle, borne in a thin- walled, calcareous tube (Fig. 117, 11). 



Fig. 117. Nautilus. (Reduced) 



1, mantle ; 2, dorsal fold of mantle ; 3, tentacles ; k, 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. (After Ludwig) l 



Oliver Wendell Holmes, in his poem "The Chambered 

 Nautilus," thus refers to the phenomena of its growth : 



Year after year beheld the silent toil 



That spread his lustrous coil ; 



Still, as the spiral grew, 

 He left the past year's dwelling for the new, 

 Stole with soft step its shining archway through, 



Built up its idle door, 

 Stretched in his last-found home, and knew the old no more. 



Fossil Relatives of the Nautilus. Many millions of years 

 ago, in the early history of the earth, the most ancient of the 

 immediate ancestors of the nautilus lived. This form had 

 a straight shell and is called Orthoc'eras. 



1 From Hertwig-Kingsley's Manual of Zoology. 



