ECOLOGY OF TADPOLES 53 



wasliing. The filters can, however, be regarded as food-concentrating 

 organs. It is possible that the need for backwasliing with clean water, 

 essential if the filter is not to be hopelessly blocked on both sides, 

 accounts for the atrium of the tadpole. This space always contains 

 filtered water, however muddy the water of the pond may be. 



It is interesting that Strawinski (1956), in giving some reasons for 

 supposing that the gill filters in R. escnk'nta have little respiratory 

 function, considers that they are often covered with food and mucus. 

 This I have never seen in R. temporaria — the filters may occasionally 

 have some particles of food upon them but never to any great extent. 

 Whether this is a species difference it is hard to say, but almost all my 

 tadpoles were anaesthetized before fixing. This was partly because I 

 dislike killing animals, but also because animals killed violently may 

 regurgitate food. I feel rather doubtful whether a live tadpole has 

 much food on the filters at any time, because they depend for their 

 functioning on being sufficiently free to pass large quantities of water. 

 I beHeve that their main nutritional function is to trap whatever misses 

 the mucous cords or centrifugal mechanisms. 



The existence of these two feeding mechanisms is another illustration 

 of the versatility of the tadpole. It can feed either on very small 

 particles or on quite large ones, and its ability to colonize many 

 different types of pond may depend on its digestive physiology. 

 Hypopachus aguae would surely starve in a pond that only had Ento- 

 mostracae as food, unless it could compete with the Crustacea for the 

 microscopic organisms. Microhyla heymonsii has a mouth shaped like a 

 funnel, and apparently specially adapted to collect the surface film. 

 It could surely not thrive except in ponds where this was abundant. 

 R. temporaria can hve in a variety of habitats. 



Respiration 



The same current of water that brings food into the tadpole also 

 serves for respiration. This is not by any means the only method, and 

 since the subject has been illuminated by an extensive research of 

 Strawinski (1956), it has now become possible to view it in the hght of 

 more detailed anatomical and physiological information than was 

 available before. The various methods have a considerable degree of 

 independence, and it sometimes seems that it is easier for purposes of 

 description to separate the different methods of respiration from one 

 another than it is to separate respiration from ingestion. 



