OBSERVATIONS AND EXPERIMENTS ON EUGLENOIDINA. 167 



TABLE II. 



COMPARATIVE NUMBERS OF SPECIMENS OF CERTAIN ORGANISMS IN THE RECTUM OF 

 TEN SPECIMENS EACH OF "NORMAL" AND "DWARF" TADPOLES OF 



Rana pipiens. 



The numbers were obtained by counting those in ten fields with a magnification 

 of 520 diameters. 



The euglenoids were thus almost entirely restricted to the 

 rectum of the dwarf tadpoles. They seemed to be in excellent 

 condition; the pigment spot was bright red; the chlorophyll 

 bodies were a brilliant green ; and swimming activities and meta- 

 bolic changes were apparently normal. 



8. Conclusions. This comparative study of 10 specimens each 

 from these two sets of tadpoles leads to the following conclusions: 



(a) The euglenoid, Species A, is a constant inhabitant of the 

 rectum of the tadpoles of Rana pipiens obtained from an alga 

 pond at Ithaca, N. Y., and a rare inhabitant of the rectum of 

 tadpoles of the same species from a neighboring alga-less pond. 

 Infection with Opalina, Trichomonas, and Hexamitus was about 

 the same in both sets of tadpoles. 



(&) Although of approximately the same age the tadpoles 

 containing many euglenoids were only about one half the size of 

 the other set; and were less advanced in metamorphosis. The 

 presence of these euglenoids may have been a factor retarding 

 growth and metamorphosis. 



II. Effects of Starving the Host on the Persistence of Euglenoids 

 of Species A in Tadpoles of Rana pipiens. After a comparison 

 was made between tadpoles of Rana pipiens one set of which 

 contained euglenoids in abundance and the other set few or none, 

 it was decided to keep infected tadpoles in the laboratory and 

 examine them at intervals to see if the infection persisted for any 



1 One or several specimens were present in 6 of the 10 tadpoles. 



