1883.] 



MICROSCOPICAL JOURNAL. 



195 



culiar manner to a strong, vertical, 

 steel wire-rope. Within the cylinder 

 there is a strainer, near the top, and 

 at the bottom there is a valve which 

 opens upwards so that water may flow 

 through the cylinder as it descends in 

 the sea, and the strainer will retain the 

 creatures that may be living in it The 

 purpose of this apparatus, which was 

 devised by Capt. C. D. Sigsbee, U. S. 

 N., is to assist in the study of the ver- 

 tical distribution of life in the sea. 

 The method of using it is as follows : 

 Suppose the exploring vessel has 

 reached a station where it is desired 

 to know the character of the fauna at 

 a certain depth — we will say between 

 100 and 150 fathoms. A sinker is at- 

 tached to the wire rope, and a few feet 

 above it a brass stop, the purpose of 

 which will soon be made clear, is 

 firmly secured. The rope is then 

 payed out until the stop is 50 fathoms 

 down, when the cylinder, or gravita- 

 ting trap as it is called, is attached. 

 The paying out is then continued un- 

 til the stop reaches the depth of 150 

 fathoms, when the trap will be at 100 

 fathoms. Down to this point the trap 

 has remained closed, and filled with 

 filtered water, quite free from living 

 forms. It is now necessary to open 

 the trap, and allow it to glide down 

 on the rope until it reaches the stop 

 at 150 fathoms, which will close it 

 automatically. This is done by send- 

 ing a conical weight, or messenger, 

 down on the wire which releases the 

 trap from its fastenings, when its 

 weight carries it down, while at the 

 same time the valve in the bottom is 

 set free and opens, allowing the water 

 to flow through the cylinder as it de- 

 scends. The organisms in the water 

 between 100 and 150 fathoms are 

 thus collected and brought to the sur- 

 face for examination. The observa- 

 tions that have been made with the 

 aid of this ingenious contrivance have 

 shown that microscopic animal life in 

 the sea is confined in depth to two 

 narrow zones, one at the surface and 

 the other at the bottom, the interme- 

 diate zone being quite devoid of life. 



On the "Challenger" expedition the 

 tow-net was used by Mr. Murray at 

 depths of 500 and even 1000 fathoms, 

 but the results were not to be relied 

 upon. The tow-net brought up livmg 

 forms in all cases, but as these might 

 have been collected near the surface 

 as the net was rising or sinking. Prof. 

 Agassiz asked the cooperation of 

 Capt. Sigsbee in devising an instru- 

 ment to settle all doubts, and the gra- 

 vitating trap was the result. 



In many places, when the water is 

 smooth and the sun brightly shining, 

 the surface swarms with pelagic forms 

 of life — annelid larvas, medusae, sal- 

 pas, radiolarians, pteropods, crustacean, 

 globigernce, algce, etc., abound, and 

 afford rich hauls for the tow-net. If 

 the surface is disturbed by winds the 

 animals descend just far enough to be 

 out of the range of disturbance. But 

 they never go down very deep, as they 

 find their food near the surface. It 

 appears that the range in depth of the 

 pelagic forms is limited to about 100, 

 or at the most 150 fathoms, and by 

 far the greatest abundance of living 

 creatures is within 50 fathoms of the 

 surface. 



In the science and art department 

 of the South Kensington Museum 

 there is a large chart of beautifully exe- 

 cuted and colored drawings, represent- 

 ing the surface oceanic life observed 

 under the microscope by Francis 

 I. Palmer, in H. M. S. "Rodney" 

 between Hong Kong and England, and 

 in H. M. Surveying Ship "Sylvia" 

 between England and Ceylon. 



The voyage of the " Sylvia " was 

 made during the time from December 

 1866 to March 1867, the homeward 

 voyage of the " Rodney " was made 

 from Sept. 1869 to April 1870. The 

 collections were made by towing nets 

 of fine gauze behind the vessels, at 

 speeds ranging up to ten miles an 

 hour. 



On this chart there are over 600 

 drawings of microscopic animals, each 

 of which is also represented by a dot 

 or mark showing its natural size. 

 They embrace a great variety of 



