ON CEPHALOPODA. 305 
as Pliny gives none of the details which are furnished by 
Aristotle; he confines himself solely to mentioning the mode 
in which it navigates, by raising its first two arms, between 
which it extends a membrane of extreme tenuity, rowing 
with the others, and steering with its medial tail, an organ 
which never existed in any species of octopus. 
Oppian, in his Halieticon, also speaks only of the first 
species of Aristotle’s nautilus, but, like a poet, he considers 
only its mode of navigation, which he believes to have served 
as a model to the man or the god who first dared to open for 
himself a path upon the waters. 
“‘ Concealing itself,” continues Oppian, ‘in a concave shell, it 
can come to land, but it can also raise itself to the surface of 
the waters, the back of its shell being upwards, lest it should 
fill with water: as soon as it has arrived at the surface it 
turns its shell, and navigates like the most skilful sailor. For 
this purpose it extends like sail-yards two of its feet, between 
which there is a thin membrane, stretched like a sail by the 
wind, while the other two, which touch the water, direct, as 
with a helm, the house, the vessel, and the fish. If it per- 
ceives any danger it furls its sail, draws in the helms, and 
plunges into the deep, being rendered more heavy by the 
water which it has caused to enter into its shell.” 
AMlian, under the denomination of polypus nautilus, like- 
wise speaks only of the first species of Aristotle, without even 
adding the second name given by Pliny. He also tells us of 
the mode of navigation, with some little variety: to come to 
the surface the animal ascends, the back of the shell being 
upwards, to prevent it from filling with water ; but once arrived 
there it turns it. Ifthe sea be calm it then navigates as in a 
small boat, rowing with two of its arms, which it has extended 
one on one side and the other on the other side of its znnate 
or connate shell; but if there should be a little wind it pro- 
ceeds by converting its oars into a strong helm, at first ex- 
VOL. XII. X 
