Invertebrate 



rapidly expanding shell of a delicate paper-like texture 

 to which the name ' paper nautilus ' or Argonaut has 



Pearly Nautilus, cut open, a, 

 partitions in the shell; l>, air- 

 chambers ; ', body whorl of 

 shell ; c, siphuncle or tube 

 communicating between the 

 air-chambers ; d, lateral mus- 

 cles attached to shell ; e, hol- 

 low arms or tentacles ;_/", ten- 

 tacles ; g, membranous disk 

 at head ; h, eyes ; z, lower 

 wall of funnel. 



been given. Other species, like the Octopus or sea- 

 spider, have no shell either internal or external. 



Anatomy. On account of the fore- shortening of 



