THE ''SAILING'' OF THE NAUTILUS. 8i 



feet, but, being highly flexible, are adapted for employment 



also as prehensile arms, with which their owner captures 



its prey, and they are rendered more perfect for this purpose 



by being furnished with suckers which hold firmly to any 



surface to which they are applied. The Cephalopods 



which have the foot divided into ten of these segments or 



arms are called the Decapoda, those which have only eight 



of them are called the Octopoda. All of these have tivo 



plume-like gills — one on each side — and so are called 



DibrancJiiata ; and in the eight-armed section of these is the 



argonaut or Paper Nautilus. Of the Pearly Nautilus and 



the four-gilled order I shall have more to say by-and-by : 



at present we will follow the history of the argonaut. 



Notwithstanding all that has 



been written of it, it is only 



within the last fifty years 



that this has been correctly 



understood. An eight-armed 



cuttle was recognised and named 



OcytJioc, which, instead of hav- '*"-"»-'-^^^.^^ 



ing, like the common octopus, ^^c;. 28.-THE paper nautilus 



{Argonauta argo) retrac- 



all of Its eight arms thong-like ted wrrniN its shell. 

 and tapering to a point, had 



the two dorsal limbs flattened into a broad thin mem- 

 brane. Although this animal was sometimes seen dead 

 without any covering, it Avas generally found contained in 

 a thin and slightly elastic univalve shell of graceful form, 

 and bearing some resemblance to an elegantly shaped boat. 

 It did not penetrate to the bottom of this shell ; it was not 

 attached to it by any muscular ligament, nor was the shell 

 moulded on its body, nor apparently made to fit it. Hence 

 it was long regarded as doubtful, and even by naturalists so 

 recent and eminent as Dumeril and De Blainvillc, whether 



G 



