Pomona College, Claremont, California 51 



Table 8. Data for Bufo americanus— -Continued 



No. Body Tail Moutli Ali. Can. Korc LcRs Lot FOOD 



24 1(1 2 " ■■ ■■ 12 ■• 3 N'othing identifiable 



25 9 2 ■' ■• ■• I J '■ 3 Kpidermis 



26 ID 1 ■• •■ •■ 13 " 3 Kpidermis 



27 1(1 1 ■• ■• '■ 11 •' 3 N'othing identifiable 



28 10 i ■• •• " 13 " 3 Kpidermis ? 



29 II 5 ■• •• ■• 13 " 3 Mud with Navicnla, masses of Plenro- 



coccus 



30 ') " ■■ •■ 13 " 2 Physopoda 1, Insecta 1 



31 11 .'; ■• ■• ■• 13 " 3 rulmonata 1 



32 10 ■• " " 16 " 3 Kpidermis, iptera larva 



33 II n •• ■• ■■ 13 " 3 Collembola 2 



34 II ■• ■■ ■■ 12 " 3 XothinK identifiable 

 3.'; II •• •• ■■12 " 3 .\othinK 



36 10 ■• •• ■• •• 10 •• 3 l';pidermis 



37 10 ■■ ■■ ■■ 10 •' 3 lipidcrmis, Diptera 1 



38 10 ■■ ■■ ■■ II •• 3 NothinK 



39 9 n •■ •■ ■■ 10 •■ 3 N'othing 



40 10 •• ■• •• 10 " 3 Kpidermis 



Comparison of Tadpoles of the \^arioiis Species. 



In the eight species used the tadpoles agree in being for the most part herbivorous. 

 The small mouth is provided with horny jaws and is used largely in nibbling off 

 Algae, bits of moss, and other plants, and in gathering up masses of ooze and mud 

 with the many diatoms and desmids to be found in such situations, and the occasional 

 Protozoa of the Difflugia and Arcella types. 



Very often one sees statements such as made by Miss Dickerson that tadpoles, 

 especially of some species, are very "fond of any animal food available. Thus these 

 tadpoles act as scavengers and dispose of dead fish or dead tadpoles even, that would 

 otherwise become a menace to the living creatures of the pond." These statements 

 might indeed be made by almost anyone who has observed tadpoles to any extent. I 

 remember when a boy of reading that a good way of cleaning a skeleton of a small 

 animal like a mouse was to place it in a pond containing many tadpoles and it would 

 soon be nicely freed from the flesh. Experiment showed this to be more or less true; 

 but although I have studied many tadpoles in the series of forms now being discussed, 

 and although these come from many different ponds, the fact that in no case was such 

 animal matter found, leads me to believe that it is not so important a source of 

 food to the tadpole as is commonly believed. 



Since all the tadpoles of the various species are aquatic and therefore in rather 

 uniform conditions, one would not expect their food to vary as much as does that of 

 the transformed individuals. The alimentary canal is invariably very long, in keeping 

 with the herbivorous habits; but almost entirely undifferentiated, no stomach nor 

 large intestine being evident. As long as the tadpole mouth is present the alimentary 

 Ganal is almost always filled with ooze and silt, a great part of which is inorganic. 

 Since the size of the mouth varies considerably with the species, one would expect it 

 to allow of more variation in food-habit than does any other one factor. I was par- 

 ticularly interested, therefore, to see what the largest animal form taken would be 

 and in which species it would be found. Unfortunately I did not have a very good 

 series of specimens with the tadpole mouth in the large bull-frog and green-frog, but 

 those examined showed almost no variation from the smaller species. One green-frog 

 did have a small crustacean (Ceriodaphnial), a meadow-frog contained a rotifer 

 (Anurfea), another had a crustacean (Cyt>ridupsu), and a peeper was found with 



