OBSERVATIONS AND EXPERIMENTS ON EUGLENOIDINA. 169 



were usually most abundant in the rectum (see Table III.) al- 

 most as numerous in the first 10 mm. of intestine adjacent to the 

 rectum, and fewer in number throughout the rest of the intestine. 

 They were not, as a rule, distributed throughout the intestinal 

 and rectal contents, but could be seen swimming about between 

 these contents and the wall. Often they occurred in large groups 

 thus giving a patchy green color to the digestive tract that could 

 be discerned with the naked eye. 



That these euglenoids also persist in tadpoles in nature was 

 proved by the examination of three specimens collected from the 

 same pond on June 24, i.e., 12 days after the first lot were taken. 

 These specimens all contained numerous euglenoids in both 

 rectum and intestine; some of the euglenoids seemed to have 

 become paler in color. The larval period of Rana pipiens is 

 from 60 to 80 days but neither the tadpoles collected on June 12 

 and kept in the laboratory until July 7 nor those collected on 

 June 24 and kept in the laboratory until July 9 increased in size 

 nor advanced in development during this time, although they 

 were about 75 days old and should have been undergoing meta- 

 morphosis. The presence of euglenoids may have been a factor 

 in this retardation of growth and development. 



III. Infection of Rana pipiens Tadpoles with Food Containing 

 Species A . Tadpoles of Rana pipiens in which there were a very 

 few specimens of Species A were collected on June 24, 1922, 

 when about 9 weeks old. On the following day 5 of these were 

 fed on the recta from ten tadpoles of the same species in which 

 there was an abundance of Species A. Previous examination of 

 tadpoles from the same lot as those from which these recta were 

 obtained gave an average number of sixteen euglenoids per field 

 (see Table II., "dwarfs"). The 5 experimental tadpoles immedi- 

 ately began to devour the recta and all of the latter had been 

 eaten by the following day and no specimens of Species A could 

 be found in the dish. Uninfected (normal) and infected tadpoles 

 were examined at intervals of one, three, five, nine, and twelve 

 days. The results obtained are given in Table IV. It is evident 

 from the increase from 0.6 per field to 4.4 per field that Species 

 A has increased in the experimentally fed tadpoles and that this 

 increase is due to the ingestion of specimens contained in the 

 recta used for feeding purposes. Since these specimens were 



