TWO-GILLED CUTTLES. 65 
ORDER DIBRANCHIATA. 
(Two-gilled Cuttles.) 
THE creatures composing this order approach 
nearest to the Vertebrate animals of all the Mollusca. 
They have a distinct brain included in a box of 
cartilage—the vanishing remains of a bony skull; 
they have large highly-coloured and complex eyes, 
protected in some species by eyelids; and ears of 
simple structure, hollowed in the cartilage of the 
rudimentary skull. They are remarkable for having 
three separate and well organized hearts, one for 
the circulation of the arterial blood through the 
body, the others for the projection of the venous 
blood through the two gills. 
Any person who has had an opportunity of ex- 
amining one of these animals in a living state, must 
have been struck with a very curious phenomenon. 
Over the whole surface of the body there are 
coloured spots which are perpetually changing their 
position and figure, running into each other and 
separating, playing hither and thither, contracting 
and dilating, appearing and disappearing, with great 
velocity and in the most singular manner. On 
close examination, it appears evident that these 
changes are owing to a fluid which moves iregu- 
larly within the substance of the skin. Even after 
death the spots continue to play for a considerable 
time, and that on small portions of the skin cut 
‘away from the rest. 
The cause of this curious appearance is not yet 
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