of New England (Cancer irroratus) ranges to a depth of nearly 500 fathoms. The Challenger Expedition selected as defining the deep-sea fauna, a depth of 100 fathoms, others have taken 500 fathoms as marking its upper boundary, and still others a depth of 1,000 fathoms. A knowledge of this life is only obtainable by means of apparatus which will bring to the surface specimens from these great depths. The chief of these instruments, aside from the sounding lead which is very inadequate for this purpose, are dredges, tangles, and trawls, of which various patterns have been devised but which may be described in general terms as follows: The dredge consists of a rectangular frame-work of iron, one edge being sharpened or fitted with rake-like teeth to plow or scrape the bottom, while a net or bag fastened to the frame serves to hold the material collected and to bring it to the surface. This is best adapted for obtaining forms which live, attached to, or burrowing in, the ocean bottom. The trawl is a similar net so arranged as to be drawn just above the bottom and is valuable for collecting fishes which swim freely through the water. The tangle consists of large masses of unraveled rope, usually attached to a chain, which, sweeping over the ocean floor, entangles spiny forms like shrimps, starfish, sea urchins, as well as forms like hydroids and sea anemones, with numerous tentacles. Somewhat different is the Tanner net. This is so arranged that it can be sent down close to any desired depth, opened there, drawn through the water and then closed again before being drawn to the surface. By means of this the fauna of any desired depth can be collected without danger of admixture with forms from other depths. Details of the construction of these and many other pieces of collecting apparatus may be found in Agassiz, 'Three Cruises of the Blake'; Sigsbee, Deep-Sea Sounding and Dredging) (U. S. Coast Survey, 1880), and in the publications of the United States Fish Commission.

Although the dredge had previously been in use in the oyster and scallop fisheries it was first employed for scientific purposes (in moderate depths) by the Danish naturalist, Otto Fabricius Müller, 1750. (In America it was first used by Henry Wheatland of Salem, Mass.) Owing to faulty observations and to a belief that life could not exist in the greater depths of the ocean on account of the great pressure and the absence of light it was long thought that animals were not to be found at depths greater than 500 fathoms. This view disregarded the fact that Ross and Sabine, 1829, claimed to have obtained living animals from a depth of about 2,000 fathoms in Baffin Bay. Little by little evidence from sounding lines and submarine cables was accumulated which tended to overthrow this belief, but its complete disproval was accomplished by the dredgings of the United States Coast Survey in the Strait of Florida, 1867, when animals were found to be abundant at a depth of 700 fathoms. This was followed, 1869, by the expedition of the English ship Porcupine, which made successful casts of the dredge in 2,435 fathoms of water. Since that time numerous deep-sea dredgings have been conducted by the various governments, the most noticeable being the cruises of the English ship Challenger, the American Blake and Albatross, the French

Travailleur and Talisman, the Russian Minineh, the Swedish Vanadis, the Dutch Barents Expedition, the German Tiefsee Expedition, and the explorations of the Prince of Monaco. The results of all these go to show that life, even of highly organized types, occurs in the greatest depths of the ocean.

Since the dredge, tangles and trawls can touch but a minute portion of the deeper parts of the ocean bottom we have, as yet, but an inadequate knowledge of the benthal or abyssal fauna for details of which the reader should consult the reports of the various expeditions previously mentioned. In general the following remarks may be made. The greater the depth, the fewer the species present. Thus in the collections of the Challenger, 2,050 species were taken in depths between 100 and 500 fathoms; 710 between 500 and 1,000; 600 between 1,000 and 1,500; 500 between 1,500 and 2,000 fathoms; 340 between 2,000 and 2,500, and 235 from depths greater than 2,500 fathoms. Again the results of the same expedition show that the number of individuals also decreases with the depth. In depths of over 1,000 fathoms the dredge rarely captured over 10 or 15 specimens of any one species, while in lesser depths hundreds of a kind are common.

The majority of the abyssal forms probably live on the surface ooze of the bottom and the minute organisms occurring in it, while these forms are in turn preyed upon by larger rapacious forms. A prominent feature of these is the frequent occurrence of phosphorescent organs which probably serve as a lure. Some are blind, some are provided with very large eyes, and it seems certain that all the light in the greater depths of the sea is produced by the phosphorescent organs. Another feature is the large size of some of the individuals. Thus while the shallow water species of the hydroid Monocaulus reach a length of but two or three inches, the deep-sea form is three feet long. It was hoped that the deep-sea fauna would reveal living representatives of extinct groups, but this hope was not realized, nothing having been found older than the horse-shoe crab (Limulus) the brachiopods, Ceratodus, the Port Jackson sharks and the Dipnoi of shallower or fresh waters.

Taking now the separate groups of living forms occurring in the deeper waters the following general remarks may be made: Plants are extremely rare and include only a few minute and inconspicuous forms. Even the lower Alga (seaweeds) so common in shallower waters are lacking. Among the sponges the so-called glass sponges (Hexactinellide) are most abundant, some of the species being enormous (3 or 4 feet in diameter). The Calenterata are represented by the giant Monocaulus, already mentioned, and by a few jellyfish and corals. Ali groups of Echinoderms occur, most noticeable being the comparatively large number of crinoids and of holothurians, many of which are strange in structure and bizarre in outline. The Arthropoda consists largely of prawns, schizopods and isopods, some of the latter being gigantic in size, and the strange sea spiders (Pycnogonids), some having slender legs extending a foot or more from the body. Crabs are rare, as are also annelids and molluscs, while a few brachiopods (and these not of the oldest types) occur. Possibly the most interest