CEPHALOPODS. 



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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. cordiformis — 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 ARGONATJTIDJE. 



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 



