192 PROCEEDINGS OF THE 



flagellates. Of animal forms there are zooflagellates and a few of 

 the smallest ciliates, rhizopods and heliozoa. The late Prof. West 

 said that very little was known about the smaller British flagellates 

 and it is often difficult to differentiate between animal and vegetable 

 forms, but probably most of them should be included in the Algae. 

 Many of the pond-dwellers, such as Daphnia, Rotifers, etc., are 

 probably dependent on the nannoplankton for food — for this reason 

 it is undesirable to add tap-water to pond-life material that is 

 required to be kept. In a lake in Austria containing abundant 

 nannoplankton a certain species of Daphnia flourished ; but in an 

 adjacent lake, where larger plankton forms were abundant but 

 nannoplankton organisms were not, the same species of Daphnia 

 did not thrive. The reproduction of the minute plankton forms is 

 very rapid, and it is probable that they play a very important role, 

 especially in the Tropics. A series of slides was then thrown on the 

 screen, showing the comparative sizes of the meshes in bolting silk 

 of different degrees of fineness, and a number of drawings of some 

 of the minute but very beautiful forms obtained by means of the 

 centrifuge. The President, in thanking Mr. Scourfield for his 

 very interesting and instructive address, regretted that rather 

 special apparatus appeared to be necessary, and asked how far it 

 was possible for a beginner to do such work, and what was the 

 minimum apparatus necessary. Mr. Paulson asked how long the 

 concentrated material could be kept, and of what the food of the 

 nannoplankton consisted. Mr. Hilton asked if any estimate had 

 been formed of the number of minute organisms in a given volume 

 of unconcentrated water. Mr. Scourfield said that it was neces- 

 sary to use a 1/10-in. water-imm. or a 1/12-in. oil-imm. objective 

 of about N.A. 1*25, and a fairly good condenser. A thin film of 

 water seemed desirable in observing the organisms. Some of the 

 organisms would keep, when concentrated, for a few days, but 

 as a rule they did not last very well. Important work could 

 be done in finding some means of permanent preservation. As 

 regards their food, the organisms were considered to be mostly 

 vegetable, and to obtain their food as plants do. Counts had 

 been made of the number present in various places under natural 

 conditions, but Mr. Scourfield could not trust himself to give the 

 figures from memory. Mr. Akehurst said that he had adapted an 

 inexpensive mechanical toy as a centrifuge. A very hearty vote 

 of thanks was accorded to Mr. Scourfield for his address. 



