472 THE OCEAN WORLD. 



These little beings share with other Cephalopods the strange faculty 

 of changing colour under the influence of some vivid impression ; hut 

 their graceful and delicate organization redeems them from the charge 

 we have brought against the cuttles. The Nautilus can blush, turn 

 pale, and show through its transparent shell its body changing in 

 sudden shades; but it never exhibits those bristling, unpleasant 

 tubercles, the hideous inheritance of the larger and coarser Cephalo- 

 pods the tyrants of the sea. 



The male Argonauts are very small, often not a tenth part of the 

 size of the females, which alone possess the shells. 



The Nautilus carries its egg in the shell, and the little ones are 

 also hatched in this floating cradle. Four species are at present 

 known : the species described by Aristotle and Pliny, and the more 

 ancient naturalists ; namely, A. argo, or papyracea (Figs. 327 and 

 329), which are inhabitants of the Mediterranean as well as the 

 Indian Ocean and the Antilles. Two others, A. tubercula, belonging 

 exclusively to the Indian Ocean, and A. laittant, which is met 

 occasionally in the Pacific and Atlantic Oceans. 



The nautilus belongs to the section of Octopoda, and the class of 

 Acetabuliferous Cephalopods, having, as the name indicates, eight 

 feet, from o/crco, eight, and TroO?, foot ; at the same time the body 

 is entirely fleshy, and without fins. The genera of cuttles (Sepia) 

 and Calmars (Loligo) belong to another section of the same class ; 

 namely, the Decapoda, because they have ten feet and a sort of 

 internal osselet, with fins, &c. 



THE DISTRIBUTION OF THE MOLLUSC A. 



WE have thought it better to treat this subject in a separate chapter, 

 for its vast and complicated nature renders it otherwise difficult to 

 handle, except in a space which would exceed the limits of this work. 

 The different genera of the organic world are peculiar to, or most 

 frequent in, certain localities, and even species and varieties have their 

 limits. This habit pervades the entire range of organisms, from the 

 lowest plants to man, whose qualities are to a great extent the type 

 of the locality he inhabits. The geography of the Mollusca is perhaps 

 the best known to science. The labours of Mr. Louis Agassiz, 



