mination for more than a fortnight as the dangers of contamination 

 from outside sources become so great that the result does not hold true 

 for the original contents of the pool. 



In making the collections great care was taken to keejo them un- 

 contaminated by using separate nets for the different pools visited on 

 one day, and by subjecting the nets to prolonged treatment with boiling 

 water before every excursion. The aquaria and the collecting vessels 

 were sterilised by treatinent with concentrated Corrosive Sublimate and 

 afterwards rinsed with boiling water. 



The reagents commonly used were; 1) for fixing, concentrated 

 Corrosive Sublimate, hot or cold, vom Rath and Osmic acid one per cent 

 solution all of which gave good results; 2) for staining, Osmo-acetic 

 methly Green, Picrocarmine, Haematoxylin and Eosin, and Picrokern- 

 schwarz. In addition to the above I have used Absolute Alcohol and 

 a dilute solution of Pormaldehyde for fixing, and for staining Alum- 

 carmine which gave beautiful results when used in a solution of one 

 part Alumcarmine to two parts water. 



In order to slow down the movements of the more rapid members 

 of the group and make their study possible a drop of a very dilute 

 aqueous solution of gelatine was used. 



It seems advisable to briefly indicate the orientation of the animal 

 that I have followed. The ventral face is that which carries the mouth, 

 and the dorsal face is the face opposite to this. If the mouth is situated 

 on one of the lateral margins, the terms used are ventral margin, dorsal 

 margin. If the Infusorian be placed mouth downwards, then the 

 anterior part is that which is directed forwards in ordinary progression, 

 and the posterior part that which is directed backwards. The sides of 

 the body are then named, the right lateral margin, left lateral margin, 

 or when necessary the right lateral face and the left lateral face. 



The division of the Ciliata into five orders has been adopted as it 

 is the most convenient, and the division into families is that of Sche- 

 wiakoff for the Holotricha and of Bütschli for the other orders. 



To give more concrete value to the terms, very small, small of 

 medium size, large and very large which are found in the descriptions, 

 I have adopted Schewiakoff's figures Avhich are as follows: 

 Very small. Infusoria whose body length does not exceed 0,04 mm. 

 Small - ------ 0,07 - 



Of medium size - _-_-__ o,12 - 



Large - ------ o,25 - 



Very large - - - _ exceeds 0,25 - 



The measurements of the species are taken chiefly from Roux and 



