OBSERVATIONS AND EXPERIMENTS ON EUGLENOIDINA. 179 



is probably not the usual method of infection in nature, since a 

 resistant over-wintering form of Species A probably exists by 

 means of which the new broods of tadpoles are infected in the 

 spring. 



(5) Attempts to cultivate Species A outside of the tadpole 

 failed and it seems probable that trophozoites are incapable of 

 living and reproducing themselves in water outside of the host. 

 Specimens were kept for several days in intestines and recta 

 that had been dissected out and placed in water and also in rectal 

 contents sealed under a cover glass. The latter proved to be 

 sensitive to light congregating on the side of the slide toward a 

 north window and moving from one side of the slide to the other, 

 a distance of 16 mm., in about 20 minutes, when placed opposite 

 this window. 



(6) An attempt was made to infect tadpoles of Rana pipiens 

 with three species of free-living euglenoids. The euglenoids were 

 all ingested but none became colonized in the digestive tract. 

 One of these euglenoids was taken from the bladders of Utricularia 

 in which they were able to maintain themselves in spite of the 

 secretions present there. The species that inhabit the intestine 

 and rectum of the tadpoles therefore possess a resistance to diges- 

 tive juices not present in free-living forms. 



(7) All of a large group of tadpoles of the toad, Bufo lentiginosus 

 americaniis, were found to be infected with Species A, but another 

 group of tadpoles of this species from another pond were not in- 

 fected. Specimens of infected tadpoles were kept in the labora- 

 tory without food for 31 days and examined at intervals. The 

 euglenoids persisted throughout this period. No apparent in- 

 crease in numbers was noted and no division stages nor cysts 

 were observed. There was no decrease in size. The organisms 

 were free-swimming and actively metabolic. The green chromat- 

 ophores, however, gradually became paler in color until the 

 specimens were almost transparent. Tnis loss of the green color 

 was probably due to the failure of sufficient light to penetrate the 

 deeply pigmented abdominal wall of the toad tadpole. 



(8) Euglenoids of Species A were also found in the intestine and 

 rectum of tadpoles of the green frog, Rana damitans. They were 

 not as numerous as in tadpoles of Rana pipiens or of the toad. 

 One tadpole that was fed on the intestines and recta of three in- 

 fected toad tadpoles became more highly infected, thus proving 



