E. J. BUTLER 13 



were kept on the bench exposed to the light, and a few worms remained alive 

 until May 30th. Thus in prolonging life, as in stimulating motion, both 

 warmth and light were favourable, the former more than the latter. 



The experiment was repeated during warmer weather, when the laboratory 

 temperature ranged from 30^ to 32°C. Worms that had been dried on the 

 host plant for 18 days were much more sluggish at this temperature when 

 kept in darkness than when exposed to light for several days after sowing in 

 water, whereas in another batch, only 7 days after collecting, there was no 

 appreciable difference. This suggests that starvation may also influence 

 activity. All were almost equally sluggish after the worms had lain in water 

 for 16 days. In a cool incubator at 23°C., in the dark, activity was much 

 reduced, but was stimulated even after 4 weeks when warm water was added. 

 Longevity was not tested in this experiment, owing to failure to keep the 

 worms from wandering. 



Wandering of TyUnchus angastus. 



When the study of this worm was first taken up, its remarkable activity 

 in water, combined with its immobility on the plant, led to the hasty conclusion 

 that free liquid was necessary to enable it to wander. The plants were natur- 

 ally examined in rooms in which the air was relatively dry, and under these 

 circumstances nothing beyond an occasional contraction of the body was 

 noticed when the worms were watched through the microscope on the stem and 

 leaves of rice. It has now been fully established by repeated observation 

 that free liquid is not necessary for travelling, but that the worms can move 

 slowly, but none the less through considerable distances, in a saturated or 

 very damp atmosphere. As this is one of the most important factors in 

 explaining the periodic incidence of the disease, it requires to be further 

 considered. 



The first indication of migration in a saturated atmosphere was obtained 

 while drops of water, containing a known number of worms, were kept under 

 observation for long periods on slides in a moist chamber. After one or more 

 days some of the worms were missing. When this had occurred several times, 

 accident revealed the missing worms on other parts of the slide, often near the 

 edge, which they apparently find difficult to pass. If examined immediatel)- 

 on removal from the moist chamber, or in slides prepared as for the well- 

 known " hanging drop " method of examination, they can be seen to move 

 slowly by a snake-like method of progression. On open slides progression 

 soon ceases when exposed to room dryness, but it starts again if the slide be 



