1897] MICROSCOPICAL JOURNAL. 245 



trap-door is also let down. The trap remains closed until 

 the bottom is reached. When the apparatus has reached 

 the required depth, then we pull the rope of the trap-door 

 and thus open it ; the tightness of the rope which before 

 was loose will inform us of the success. Then we must 

 give our boat a slow impulse and drag the net along as 

 fig. 7 shows. The water with all its organisms and the 

 mud tilled up by the scraper, will then fill the dredge. 

 Before drawing out the net, we let loose the rope of the 

 trap door, thus closing it ; no other material can there- 

 after penetrate into the net. The exact closing of the 

 trap is furthered by the two brass-sticks. According to 

 their length they allow the opening of the trap only to a 

 certain height, viz., to about 20-25" to the upper board 

 of the frame not in a vertical position. Thus the closing 

 of the trap-door is not only due to its own weight, but 

 also to the pressure of the water. After drawing up the 

 net, the trap door is opened, the net turned inside out 

 and the material washed into the bowl. According to 

 the directions already given, it is then put into the con- 

 serving liquid and finally into the cylindrical glass. 



The attention of naturalists is called to a great advan- 

 tage which this net possesses over the drag and bottom- 

 nets hitherto described. It enables him to undertake the 

 exact determination of species living in different levels of 

 water. With this implemeiit, the opening of its trap- 

 door being under control, we may collect our material at 

 depths corresponding to our desire and state exactly the 

 presence and migration of such and such species. We 

 may determine in which masses or swarms they occur, 

 during the different parts of the day ; even the hour and 

 the different depths in which they wander. 



We have also to equip ourselves with certain other 

 necessary things. It is very convenient to use a hunter's 

 pouch. In the place of the cartridges we put our glass 

 tubes and in the pouch itself the bowl and smaller nets. 



