Dakin and Latakche — The Plankton of Lough Neagh. 31 



strikes with force the bolt h, and as a consequence the bolt is depressed. 

 This sets free the jaw/, which revolves, and allows the ring supporting the 

 net-mouth to fall out (fig. 3). As a result the net falls away until the 

 throttling rope becomes taut, tightens round the net, strangling it, and 

 supports it in such a position that if the net is now pulled thi'ough the water 

 it can neither catch nor lose anything (fig. 2). 



Fig. 3. — Closing Mechanism of Net with Fig. 4. — Closing Mechanism of Nansen 



Messenger. Net. 



The depth of water at the observing station was 40 feet. The net was 

 used open all the way from the bottom to the surface, the catch being thus 

 taken from the whole column of water. In addition to this, catches were 

 taken from the top 20 feet, the top 10 feet, bottom 20 feet, and bottom 

 10 feet of water. The method of procedure for the bottom 20 feet and the 

 top 20 feet is essentially the same as that for the bottom 10 feet and top 

 10 feet. To catch the organisms in the bottom 10 feet, the net is attached 

 to the closing mechanism and lowered open, care being taken that the descent 

 is perfectly vertical. It is lowered until the mouth is one foot above the 

 bottom. This is determined by sounding first to note exactly the depth. 

 One can then easily lower the net to the correct point by observing the line 

 paid out, which should be marked off \i\ half fathoms. The net is next drawn 



