CEPHALOPODS. 
33i 
Other Families. 
creature changes its colour is amazing. At the slightest disturbance a dark 
shade passes with the rapidity of lightning over the whole body. When it seizes 
its prey its entire skin becomes yellowish, studded with blackish symmetrical spots, 
and covered all over with conical tubercles. These molluscs have a strong musky 
smell, but in spite of this they are not unfrequently seen in the Italian markets, 
and purchased by the poorer classes. 
Other octopods are Cirroteuthis, Pinnoctopus, Tremoctopus, 
Amphitretus, and a few other allied genera, and Argonauta, several 
of which represent families by themselves. In Cirroteuthis the arms are con¬ 
nected throughout their entire length with a thin membrane, forming a sort of 
umbrella, at the bottom of which is the mouth. They are furnished with only a 
single row of suckers down the middle, but have a series of short cirri on each 
side, and the body is provided with two lateral fins. Seven species of this genus 
are known at present. C. maura was captured at a depth of thirteen hundred and 
seventy-five fathoms, and C. pacifica , off New Guinea, in two thousand four 
hundred and forty fathoms. C. muelleri, the type of the genus, occurs on the coast 
of Greenland. Pinnoctopus is remarkable for a fin-like expansion, extending the 
whole length of the body and uniting behind. In P. corcliformis —the only known 
species, and an inhabitant of the shores of New Zealand—the arms are long, and 
united at the base by a somewhat large membrane. Tremoctopus has no lateral 
expansions or fins to the body. The female has the two dorsal pairs of arms 
united by membrane, the two other pairs free; the male is without the interbrachial 
web; the head is large, having two pores on the upper and under sides. Nine 
species altogether have been described from the Mediterranean, North Atlantic, and 
Pacific. The genus Amphitretus is one of the remarkable forms obtained during the 
Challenger expedition. It possesses the character, unique among cephalopods, of 
having the mantle fused with the siphon in the median line, so that there are two 
openings into the branchial cavity, one on either side, whence the name. 
Family ArgoNAUTIDJE. 
The argonaut, or paper-nautilus, is one of the most interesting of the octopods, 
for around it for many years there hung a mystery and uncertainty. Some con¬ 
cluded that the shell was formed by another mollusc, and was merely taken 
possession of by the cephalopod, as a convenient abode or boat to swim in, or 
rather to sail in, for it was stated to raise aloft its two expanded arms to catch the 
breeze, and thus to voyage onward. This, for many years, has been proved to be 
mere fiction. The shell, with which only the female is provided, is of her own 
manufacture, and she swims just the same as other cephalopods. It is large, not 
adhering to the body of the animal, but retained in position by the application on 
the outside of the dorsal pair of arms, which are dilated and especially adapted for 
the purpose. Whether the argonaut ever quits its shell voluntarily or only 
by accident is unknown; specimens have been captured at sea without any shell, 
and they have lived for some time in that condition. A specimen was placed in an 
aquarium at a time it was out of its shell. This it re-entered, and remained in it 
the whole period, about fifteen days, it was in captivity. It invariably swam at the 
