166 ROBERT W. HEGNER. 



of the two groups of tadpoles differed in appearance, the differ- 

 ence being due apparently to the presence of algse in the dwarfs 

 and the absence of algae in the normals. The intestines of the 

 latter were filled with very fine particles of mud mixed with 

 diatoms and minute organic debris; they were grayish in color, 

 of uniform thickness, and smooth in outline. The intestines of 

 the dwarfs, on the other hand, contained large pieces of algse 

 which appeared to divide the contents into separate masses, 

 giving the entire intestine a patchy appearance; they were slightly 

 tinged with green, and had an irregular outline due to the irregular 

 distribution of the contents. The organisms noted in the intes- 

 tines of both sets of tadpoles included a very few normal inhabi- 

 tants of the rectum Opalina, Trichomonas, and Hexamitus; at 

 least 60 per cent, of both sets were inhabited by Giardia agilis; 

 euglenoids were found in four of the dwarfs and one of the nor- 

 mals; and filamentous algae were present in considerable abund- 

 ance in all of the dwarfs but in only one of the normals. 



7. Character of the Contents of the Rectum. The contents of 

 the rectum of the normal tadpoles gave this part of the alimentary 

 canal a grayish appearance, but in the dwarfs the euglenoids 

 were so abundant that a distinct greenish color was produced. 

 It was difficult to count accurately the number of specimens of 

 the various organisms present. The method employed was to 

 mix thoroughly on a slide the entire rectal contents in one drop 

 of normal saline solution ; spread this out under an 18 mm. square 

 cover glass and count the number of organisms in ten separate 

 fields in different regions of the slide using a 4 mm. objective and 

 a 4 X ocular. Averages for each tadpole were then computed. 

 Table II. gives the range and the average numbers of five different 

 organisms. Endamcebce and other forms were encountered but 

 were not recorded. Opalina, Trichomonas, and Hexamitus were 

 present in every tadpole and no significant differences in number 

 were noted. The most conspicuous difference in the two groups 

 of tadpoles was the presence of large numbers of euglenoids and 

 of considerable amounts of filamentous green algae in every one 

 of the dwarfs and the almost complete absence of these in the 

 normals. One or several euglenoids were found in the rectal 

 contents of six of the normals after long searching and a little 

 algae was seen in one of them. 



