OBSERVATIONS AND EXPERIMENTS ON EUGLE- 



NOIDINA IN THE DIGESTIVE TRACT OF 



FROG AND TOAD TADPOLES. 



ROBERT W. HEGNER. 



On a number of occasions during the past decade the writer 

 has observed living flagellates of the Euglena type in the intestinal 

 and rectal contents of frog tadpoles. They were always consider- 

 ed merely accidental inhabitants that had been ingested with the 

 food of the tadpoles and were either immune to the digestive 

 juices and were on their way through the intestine or had not 

 yet succumbed to digestion. The observations and experiments 

 described below, however, furnish evidence (i) that these flagel- 

 lates are of widespread occurrence among the tadpoles of a numb- 

 er of species of frogs and toads, (2) that they are normal inhabi- 

 tants of the intestine and rectum of tadpoles in the same sense 

 that the better known protozoa, such as Opalina, are, (3) that 

 they persist in starved tadpoles for many days, even after 

 Opalina has disappeared, (4) that they retain their green color 

 for a considerable period within the body of the tadpoles, (5) 

 that they can be transferred in the trophozoite stage from one 

 species of tadpole to another with food material, (6) that they 

 differ in structure from any free-living or parasitic Euglenoidina 

 heretofore described, (7) that they do not grow and multiply 

 easily under ordinary culture conditions, (8) that certain free- 

 living species of Euglenoidina are digested by tadpoles that do 

 not digest the entozoic species, and (9) that certain tadpoles 

 that were heavily infected with Euglenoidina did not become 

 full-grown and undergo metamorphosis. 



i. A Comparison of Normal Tadpoles of Rana pipiens with 

 Tadpoles Containing Large Numbers of Species A. The first 

 series of observations, recorded in Table I. indicate that the 



1 From the Department of Medical Zoology, School of Hygiene and Public 

 Health, Johns Hopkins University. The writer is indebted to Dr. Hugh D. Reed 

 for the privilege of working in his laboratory at Cornell University during the 

 summer of 1922. 



162 



