THE TWO-GILLED GROUP 3299 



having separate life, and continuing to exist for some time after being transferred to 

 her keeping. The lost portion of the hectocotylized arm of the male is gradually 

 reproduced, and in due time assumes its former appearance. 



A second group of octopods (Eledone), which occurs in the Mediterranean and 

 also on the British coasts, differs from the common octopus in having but a single 

 row of suckers down each arm. In E. moschatus the body is very changeable in 

 form, pouch-like, oval, rounded, or pointed behind, smooth or warty, just as the 

 animal likes. The great size of the mantle opening, which extends a little over the 

 back, is also remarkable. It is of a gray, yellow, or yellow-brown color, with black- 

 ish spots, and a bluish edge to the web, and is met with on sandy and gravelly 

 bottoms at all times of the year, more rarely among rocks. The rapidity with 

 which the creature changes its color 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 mollusks have a strong 

 musky smell, but in spite of this they are not unfrequently seen in the Italian mar- 

 kets, and purchased by the poorer class. 



Other octopods are Cirroteuthis, Pinnoctopus, Tremoctopus, Am- 

 phitretus, and a few other allied genera, and Argonauta, several of 

 which represent families by themselves. In Cirroteuthis the arms are connected 

 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. Tremodopus 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 characteristic, 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 ARGONAUTID^G 



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- 



