8o Micro-Fauna, Botanic Gardens Lake, Melbourne. [voLXXxv. 



water from a reservoir in Studley Park, which is filled from a 

 pumping station on the Yarra, near Dight's Falls, and there- 

 fore it must receive from time to time importations from the 

 reaches of the river higher up. 



The first visit of the series was made on 26th June, 1915, 

 when an excursion of the Microscopical Society was held. 

 Afterwards the visits were made approximately fortnightly for 

 a year, the last of the series being on 9th June, 1916. The 

 dates of the visits only varied a day or two either way from 

 the exact fortnightly interval. 



It was early noticed that the better swimmers among the 

 plankton were found diffused throughout the lake, and special 

 attention was given to these in order to find indications of 

 periodicity of occurrence. The examination was largely directed 

 to this aim. The material was taken home and searched over 

 as soon as possible — Mr. Searle specializing on the Ento- 

 mostraca, Mr. Stickland the Protozoa, and Mr. Shephard dealing 

 with the Rotifera. Early examination is specially necessary 

 in the two last-mentioned groups, as, when crowded in the 

 jars, it was found that forms extremely plentiful on collection 

 would disappear in a few hours and leave no trace. As already 

 stated, preservation of the material was not attempted to any 

 extent, attention being focussed chiefly on recording the 

 occurrence of the various forms observed. Estimates of the 

 relative prevalence of the forms were made. 



The material obtained would have occupied the whole time 

 of several workers to fully deal with it, and, as the work was 

 effected in the leisure time of those concerned, it will be under- 

 stood that the list of actual identifications of the groups 

 mentioned by no means represents the whole of those to be 

 found in the lake. It is manifest that sedentary forms collected 

 round the margin from a few positions could not be relied on 

 to give accurate results as to their prevalence at a given time 

 throughout the whole lake, the number of such found on a 

 given occasion being more dependent on the diligence of the 

 collector than the actual occurrence of the animals themselves. 

 A sedentary form cannot spread rapidly, and may occur on 

 the plants at one part of the shore and be entirely absent at 

 another. If, however, a sedentary form is found in every place 

 tried, and on a number of successive visits, it must then be 

 regarded as prevailing throughout the whole area. Such a 

 case would be an exception, and such were found. 



Vorticella campanula was on several occasions found on every 

 bit of stick or weed examined over a large area. Cordyllophora 

 lacustris also occurred in this way. This latter form, known for 

 many years as an inhabitant of this lake, seemed to disappear 

 for something like fifteen years, but was, during the whole 



