THE FIRST ALBATROSS EXPEDITION 263 



That we had worked hard was seen at the end of our 

 trip. At Guaymas, when I left the ship, we were neither 

 of us in condition to do another stroke of work." 



During this cruise Agassiz made a special study of 

 vertical distribution of pelagic fauna, or the depth to 

 which floating animals may be found beneath the sur- 

 face. Some naturalists, especially the staff of the Chal- 

 lenger, and more recently Dr. Chun, had reached the 

 conclusion that animal life extended to great depths in 

 the ocean. 



But the Challenger experimented on this question 

 only during the last part of her cruise, and did not use 

 nets that could be closed before being drawn up, so that 

 they might collect anything on the way to the top of 

 the water. This is the so-called differential method, 

 which Agassiz always regarded with the greatest dis- 

 trust. For example, suppose that an open net is drawn 

 up vertically from one hundred fathoms, and a second 

 from two hundred fathoms. By this method it is as- 

 sumed that anything found in the second net that was 

 not in the first net must come from between one hun- 

 dred and two hundred fathoms. Dr. Chun used a net 

 which, after being towed at a given depth, could be 

 closed before being drawn to the surface. But most of 

 his work was done in the Mediterranean, where the 

 conditions are entirely different from those in the open 

 sea, and he himself says he had difficulty in closing his 

 net properly. 



It will be remembered that in his cruises in the Blake, 

 Agassiz had investigated this question with the Sigsbee 

 Gravitating Trap, by means of which it was possible to 

 filter a column of water of any desired height at any 



