Introduction 7 



as food by Amoebae, Turbellarians, Oligochaetes, Tardigrades and 

 Crustacea. The tadpoles of the common frog feed almost exclu- 

 sively on the larger filamentous Algae, and Bles has recently shown 

 that the larvae of that most remarkable African frog, Xenopus 

 Icevis, feed exclusively on the lower Algae 1 . A considerable pro- 

 portion of the food of freshwater Lamellibranchs also consists of 

 living and decaying Algae. 



For the collection of freshwater Algae a plentiful supply of 

 small wide-mouthed tubes or bottles will be found most useful. 

 Small quantities of the larger, strictly aquatic Algae should be put 

 into these tubes, care being taken not to overstock the tube. A 

 small tuft of the Alga with plenty of water is best, and the tube 

 should not be filled more than three-quarters full. The reason for 

 this is obvious, as rapid decomposition accompanies overcrowding, 

 and it frequently happens that collections cannot be examined for 

 many hours after they have been made, or under certain circum- 

 stances even for a day or two. 



To collect the minute Algae that occur attached to larger water 

 plants, the latter should be removed from the water with as little 

 mud as possible, the superfluous water allowed to drain away for a 

 few minutes, and they should then be gently squeezed over a wide- 

 mouthed bottle, the issuing water being collected in the bottle. 

 In the sediment which settles to the bottom of the water in the 

 bottle will be found numerous unicellular and other small Algae. 

 Sometimes a hundred or even two hundred species may be obtained 

 from a small quantity of such material. The Algae of the plankton 

 are collected from the surface layers of water by means of silken 

 tow-nets. 



If it is desired to keep the plants living for some time they 

 should be placed in wide-mouthed jars with an abundance of 

 water, and not exposed to too strong light. Sterile species of the 

 Zygnemaceae and (Edogoniaceae will often become fertile under 

 these conditions. 



1 There can be little doubt that a portion of the food of Ceratodus, the Australian 

 mud-fish, consists of Algse. An examination of the intestine of this fish (for which 

 I must express my indebtedness to Prof. Howes), revealed masses of sticks, twigs, 

 leaves, fragments of Hepatics, etc., all of which would have been taken in by the 

 fish from the muddy bottom of the water in which it lived. This material would 

 be mostly in a dead condition before being swallowed and it seems to suffer little 

 change in its passage through the gut ; but a microscopical examination shows 

 amongst it the decomposed remains of many kinds of Algae, including thousands 

 of the empty valves of Diatoms. 



