208 ANNIK I'Oin'EU. 



by the attacking ked. By this cannibalistic liabit it is 

 possible for Melophagus ovinus to acquire practically 

 every stage of Crithidia inelophagia direct, and this is 

 probably a subsidiary method of spreading the parasite. 



Environmental Effects. 



Crithidia melophagia shows less response to slight 

 changes of environment than does C. gerridis or Her- 

 petomonas jaculum, both of which I have studied. Never- 

 theless, under certain conditions remarkable effects have 

 been produced by relatively simple means, and these may now 

 be recorded. 



(1) Response to light. — Increased intensity of white 

 light produces increased velocity of movement of Crithidia 

 m e 1 op h a g i a . 



Green light somewhat retards the movements of the 

 organism. This is also the case with Herpetomonas 

 jaculum. 



Intense light causes aggregation-rosettes of C. melo- 

 phagia to separate. 



G. melophagia lives very much longer in diffuse light 

 than in bright light. 



(2) Responseto changes of temperature. — C. melo- 

 phagia can live at a temperature just below that of the 

 blood of the sheep, but the flagellates ai"e killed at a tem- 

 perature above 40^ C. 



At room temperature (15° C.) the parasites will live for 

 several hours. 



(3) Response to change of medium. — Though the 

 flagellates normally live surrounded by fluid blood (a discus- 

 sion of which will be given in Appendix III), yet they can 

 live in other media and can resist the effects of such media 

 to varying degrees. 



(a) Tap-water when added to the parasites in the gut- 

 liquid seemed to have little effect. Though the movements 

 of the flagellate became slightly more active, this was possibly 



