With the tow net, marine biologists were 

 able to collect microscopic plants and 

 animals from any depth. An Inner net 

 traps the specimens within the larger 

 net which has a collecting jar attached 

 to the trailing end. 



immediately. Both were hastened by discoveries in other fields. One 

 such discovery was that a simple sounding line could be used to 

 bring up samples of the bottom, as was done by Captain Phipps on 

 Cook's second voyage. As late as the early nineteenth century 

 there were those who maintained that it was unlikely that life 

 would be found below 300 fathoms. Then, in 1845, J. M. Brooke, 

 a young midshipman in the U.S. Navy, hit on the idea of fixing a 

 hollow tube device (in this case a quill) to the sounding lead when- 

 ever it was used for its ordinary purpose. He easily managed to get 

 mud and ooze from depths of 1000 fathoms or more, and to report 

 to the world that the mud contained microscopic shells. 



Had the inhabitants of the shells lived on the bottom, or had 

 the shells fallen to the bottom after the death of the animals? Today 

 it is hard to understand that such a question could have seemed 

 debatable, but it was debated until findings made possible by the 

 tow net settled the question. 



With the nineteenth century's advances in techniques, it at last 

 became possible to work out the life histories of many marine 

 animals. This had enormous importance for the fisheries research 

 programs that were soon to play a vital part in increasing the 

 world's food supplies. Once the researchers could understand the 

 food chains upon which life in the sea depends, they could make 

 good use of their knowledge. Furthermore, the identification of 

 animals brought up in tow nets was soon to make it apparent that 

 the currents in the ocean could be plotted and their movements 

 determined by a scientific study of plankton. And another impor- 

 tant idea began to emerge: that there is an orderly distribution of 

 plants and animals in the sea, just as there is on land. So the marine 

 biologist, who until 1845 had been satisfied with merely listing 

 and describing the sea dwellers, now began to map out their habitats 

 with precision. 



The earliest tow nets were simply let down into the sea, towed 

 through the water for a while, then hauled to the surface, where 

 the contents of the bucket were examined. This method had a big 

 drawback. To bring to the surface a net that had been towed 

 horizontally at a depth of 100 fathoms meant hauling it up vertically 



Brooke's cannon-ball core sampler. The ball's 

 weight drove the hollow rod firmly into the 

 sea bed. Reduced tension on the line released 

 the ball, permitting the rod to be withdrawn. 



Map on the following pages shows by colors k 

 distribution of sediments over the sea ^ 



floor. "Terrigenous" deposits are 

 generally coarse and derive from the land. 

 In contrast, fine "pelagic" deposits are 

 found in the deep sea and derive largely 

 from the skeletal remains of marine 

 creatures. (See key to map.) 



93 



