18 THE VOYAGE OF H.M.S. CHALLENGEK. 



The Toiv-Nets. — The nature and source of the deposits at present in process of 

 formation on the bed of the ocean was one of the most interesting problems with which 

 we had to deal, and we soon found that while over a large part of the area of the ocean 

 the deposits consisted mainly of the hard parts of animals, the closest relation existed 

 between the animals included in the bottom deposit of any particular area, and the fauna 

 of the over-lying water of the same area. This observation, which we had daily oppor- 

 tunity of repeating and verifying, gave a special interest to the study of the fauna, 

 principally microscopic, of the surface and of intermediate waters ; and observations with 

 the tow-net were prosecuted by Mr Murray with the utmost perseverance and care 

 throughout the voyage, so that almost every sample of the bottom taken from the sound- 

 ing-tubes is supplemented in our collection by a bottle of surface organisms from the 

 same spot preserved in spirit ; and in many cases by a series of such specimens taken 

 from different depths. 



The tow-nets were of the ordinary form, conical bags suspended from rings. The rings 

 were made of f-inch round rod-iron, and were 12, 14, 16, and 18 inches in diameter. 

 They were painted and then covered with unbleached cotton or duck, with a margin of 

 the cloth left at one side to which the bag could be sewn. The nets were of fine book- 

 muslin, of cotton bleached or unbleached, or of buntine. A ring 12 or 14 inches across 

 bore a net 4 feet 6 inches long, and for wider rings the length of the net ran up to 5 feet 

 3 inches. The net tapered from the ring to a width of 16 inches at the bottom, into 

 which a disk of the muslin or other material was sewn to facilitate the transfer of the 

 contents of the bag into a glass jar. Three cords, -fths of an inch round, were made fast 

 to the ring at equal distances and met 4 or 5 feet in front of the ring in a loop to 

 which a suitable length of sounding-line was attached for dragging the net. A muslin 

 bag was used when we were moving very slowly — ^less than two knots an hour — through 

 the water ; when we were going faster the stronger or more open (buntine) net was 

 employed. 



When it was wished to sink a tow-net a short way beneath the surface, a hand-lead of 

 12, 14, or 20 lbs. was fastened to the line a few yards in advance of the net, and the faster 

 the ship was moving through the water the heavier was the weight used. Sometimes two 

 or three nets were attached to one line at various distances along it, and sometimes nets 

 were attached at different points along the dredge-rope during its descent ; but these 

 attempts to take samples of the fauna from different horizons were rarely successful, 

 and we found that by far the best way, both at intermediate depths and at the surface, was 

 to use a single net at the end of the line and to tow it as slowly as possible. The tow-net 

 is most readily worked from a boat ; when the ship was going more than three or four 

 knots it was found impossible to use it with advantage. The tow-net was emptied by 

 putting the hand as far into the bag as possible and turning the end of the bag inside 

 out in a large glass vessel of sea-water, and shaking it well without touching its contents. 



