36 ROUSSEI.ET : 



the bottles filled with 7 per cent, formalin. This is repeated 

 four times to get rid of all traces of osmic acid and also float- 

 ing particles of dirt, and then the tube is corked as full of 

 fluid as possible, after placing in it a slip of paper with a 

 number and date and place of collection written with pencil. 

 In order to obtain also some of the loricated Rotifera fully 

 contracted, it is advisable to add to the tube a pipette full of 

 the unnarcotized living forms immediately after the osmic 

 acid has been added, as certain characters are better seen in 

 the fully contracted animals. 



B. -SEMI-PELAGIC ROTIFERS, 



that is, forms which are found mostly creeping on, or tem- 

 porarily attached to aquatic plants, are best obtained by col- 

 lecting a quantity of these plants (Ramrncnlus, Myriophyllum, 

 CeratophylbDH , Anacharis, moss, etc.) and placing these in a 

 large vessel with just sufficient water to cover the plants. By 

 allowing this to remain (not in the sun) for several hours, or 

 over night if necessary, all the animals will be driven by 

 asphyxiation to near the surface, and towards the light side of 

 the vessel, where they can be picked up with a pipette, and 

 prepared as before. 



C. FIXED ROTIFERS. 



These are more difficult to prepare, and must be treated 

 individually to obtain satisfactoiy results. However, small 

 twigs of weeds on which such Rotifers can be perceived with 

 the lens may be fixed and preserved (with or without narcoti- 

 zation) for identification. 



D. FINALLY, 



it is advisable to dry some of the weeds, particularly aquatic 

 moss (without squeezing out the water). Some Rotifers can 

 be hatched from eggs after a prolonged state of dryness. 



RAPID PRESERVATION. 

 Should want of time or other circumstances prevent the 



