240 RESEARCH IN PROTOZOOLOGY 



off free oxygen (C/., Cleveland, 1925) ? Try introducing by mouth, 

 by anus, and with both adult and tadpole hosts. Can the parasites 

 be thus destroyed without injury to the hosts? 



3) The effects of different foods for the hosts upon their 

 opalinids? Use both adult anura and tadpoles. Try protein diet on 

 each, also carbohydrate diet (Cf., Hegner, 1922, 1924). Do the 

 vegetarian tadpoles give different results from the carnivorous 

 adults ? Under conditions in which protein diet favors the opalinids 

 must fat be included in the food (Cf., Stephanson's experience in 

 the Arctic) ? If so does the kind of fat present make a difference? 



4) Study the effects of different sorts of bacteria in the intes- 

 tine upon the opalinids (Cf., Hegner, 1922, 1924; Cleveland, 

 1928). This is involved in food experiments. Of course the opali- 

 nids do not ingest bacteria or any other solid food. 



5) Effects of drugs administered to the hosts? 



6) Digestion. Do opalinids extrude digestive fluid into the 

 cecum of their host, which acts in this blind pouch as an extra- 

 cellular digestant, as Konsuloff (1922) claimed on wholly in- 

 sufficient evidence, if any? 



7) Excretion. The morphology of the excretory organs might 

 well receive more extensive study (Cf., Metcalf, 1907, and Kon- 

 suloff, 1922). Of especial interest is Metcalf 's description of 

 differentially staining granules associated with the posterior vesicle 

 of the excretory system, and their actual extrusion when this con- 

 tracts. This deserves further study. Is the process normal or 

 abnormal? Is this system of organs truly excretory? Under what 

 environmental and physiological conditions does the system in- 

 crease in extent and under what conditions is it diminished? 

 Experiment upon some of these problems is difficult without cul- 

 tured animals. 



8) Investigate the stimuli which induce rapid division of the 

 opalinids and their encystment previous to the egg-laying period 

 of the adult host (Cf., the section Host-specificity). How do these 

 conditions as to opalinids in adult anura compare with those 

 affecting opalinids in tadpoles, which, of course, form no mature 

 sexual products, but whose parasites encyst and pass to the water 

 (Rana catcsbeiana, R. clamitans and other species) ? 0) Is there in 

 these tadpoles a special season of rapid division and encystment of 

 the opalinids, or is the cyst- forming of the parasites more generally 

 distributed through the whole tadpole stage of the life history of 



