SQUIDS, ETC. 



as the animal grows, the last one occupied always being 

 walled' up or divided off by a partition called a septum. The 

 center of all the divisions is penetrated by a tube ; so, 



though living in the 

 last chamber, the ani- 

 mal is still connected 

 with the first by a long, 

 delicate, fleshy pedicle 

 that extends through it. 

 The different air-cham- 

 bers are filled with gas, 

 and by them the spe- 

 cific gravity of the ani- 

 mal may be increased 

 or diminished. Beneath 

 the mouth is a siphon 

 through which water is 

 ejected, thus forcing 

 them along. On the 



FIG. 75. Section of Nautilus pompilius, 

 showing the chambers and connecting 

 tube containing the fleshy pedicle. 



bottom they crawl with 

 the shell upward. They 

 have no ink-bag, and 



in the female the tentacles or arms number ninety-four. 



The great fossil Ammonites, three feet across, are extinct 



relatives of the nautilus. 



VALUE. Shell in ornamental work. 



NOTE. The eye of the nautilus is remarkable in having no diop- 

 tric apparatus, being merely an elevation bearing a minute hole that 

 leads into the globe of the eye, which during life is filled with sea- 

 water, and thus, according to Hensen, in place of a refracting lense 

 and cornea, there is an arrangement for forming an image on the prin- 

 ciple of the pin-hole camera. 



Order II. Two-gilled Cephalopods (Dibranchiata) ; 

 Spirilla (Sptntlidcs). These small Cephalopods resemble 

 squids, but contain within their bodies a delicate cham- 

 bered pearly shell with separate whorls, the various rooms 



