210 DAVID BRYCE ON THE 



this difficulty to Mr. Harring, of Washington, and he most kindly- 

 sent me a special metal tube, to take the place at the foot of the 

 net of the customary glass tube. The metal tube measures 

 3J inches in length, and IJ inch in diameter. At the lower 

 end it is closed. At the upper end it is provided with an easily 

 detachable and closely fitting rim, which is permanently attached 

 to the outer net in the same way as the usual glass tube or bottle. 

 The body and the rim of the metal tube are held together by 

 two bayonet catches (one at either side), which can be readily 

 disconnected, thus allowing the contents of the tube to be 

 poured into another receptacle. The metal tube has the further 

 advantage of avoiding the risk of breakage of the glass tube — 

 always at the least opportune moment— when the net is used 

 in ponds with a stony bottom. The whole arrangement is easy 

 to work and is effective in permitting the contents of the tube 

 to be secured without displacing or leaving unfastened the inner 

 net. 



I believe that a fitting has been devised whereby the " catch " 

 is received into a short metal tube provided with a stop-cock, 

 but as a part of the latter projects considerably beyond the 

 surface of the tube, I imagine the arrangement to have disad- 

 vantages as compared with that now described. 



But while the single or double net will secure a large propor- 

 tion of the species of Rotifera living in a given pond, it will not 

 secure all. Besides those species which swim, or which creep 

 over or perch temporarily upon water-plants, there is the impor- 

 tant and interesting group of rotifers which take up a per- 

 manent position on suitable plants, in many cases secreting or 

 constructing for themselves a sheltering tube ; and again another 

 group, which seek their food among the detritus at the bottom 

 of the pond. The former group are usually captured by bring- 

 ing home portions of water-plants, and for this purpose a selec- 

 tion of suitable portions is generally made at the pond-side with 

 the help of a pocket lens. There is perhaps no method of col- 

 lecting rotifers which requires more judgment and experience. 

 Great assistance is given by the use of a suitable receptacle for 

 the plants that are thus being looked over. One of the most 

 prominent members of our Club some thirty years ago used for 



