410 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



funnel-shaped flask with some light-proof material, and direct all the 

 light that can be gathered by a bullseye on to the cylinder which con- 

 tains the glass spigot. Any swimming phototactic organism in the 

 water will at once react and pass into the well, which is brightly illu- 

 minated — usually 10 to 15 minutes is sufficient to allow for this, but 

 longer time can be given if necessary. Give the spigot half a turn 

 and, as already explained, this locks the creatures in the well. The water 

 can then be poured off from the flask, the spigot withdrawn, and the 

 rotifers, or whatever may have been trapped in the well, can be taken up 

 with a pipette and transferred to the slide for examination!. After the 



Fig. 44. 



first catch has been taken the trap can be set again and a second lot 

 secured. Work can therefore be carried on without interruption or loss 

 of time until all the water has been dealt with. Should there be any 

 sediment, this can be allowed to settle and then trapped off before any 

 attempt is made to catch the organisms. 



There is difficulty in obtaining this trap made in glass, so another 

 has been worked out in metal (fig. 44). This consists of a round box, 

 1 in. deep, 3^ in. diam., the top and bottom slightly convex, mounted 

 on a tripod. A hole in the bottom allows the water to pass through a 

 short tube, which is in three sections, the first part metal, the second 

 rubber, and the third glass. A pinch-cock can be applied to the rubber 

 connexion, which will prevent water passing when the glass tube has 



