MOVEMENTS, ETC., OF ERESH-WATER PLANARIANS. 695 



in the middle line from in frunt backwards 1 have never been 

 able to obtain any definite results. They simply squirm 

 about in an aimless way for a moment when the current is 

 made and then become quietj and remain so while the current 

 passes. 'J'he directi(.)n in which the current is flowino- makes 

 no difference in their behaviour. All operated specimens 

 become very quickly paralysed by the current. 



d. Summary. — The constant current very quickly para- 

 lyses planarians. Its specific effect is to cause a contraction 

 of the anode side or end of the body. This produces in the 

 case of fresh specimens a well-defined orientation, with the 

 anterior end towards the kathode. All progressive move- 

 ment after the making of an effective current is by the crawl- 

 ing method, the cilia being stopped or very greatly slowed 

 in their beat. The electrotactic reaction, so far as the attain- 

 ment of orientation is concerned, is essentially the same as 

 the negative reaction to mechanical stimuli. In the rhab- 

 docccle S t en o stoma leu cops there is found to occur a 

 reversal of the cilia on the kathode half of the body, such as 

 occurs in the case of the Infusoria. 



V. Reaction to Desiccation. 



A series of experiments was performed to determine the 

 reactions of the animal on drying. This is an environmental 

 condition Avliich planarians probably have had to meet with 

 relative frequency in the course of their history as a species, 

 and it is a matter of interest to determine whether they have 

 any method of reacting which protects them from it. 



Experiments were first performed iu the following 

 manner : — Sjiecimens were taken from the aquarium dish on 

 the point of a scalpel or a spatula, and lightly touched to a 

 filter-paper for a moment to remove any adherent water, and 

 then laid upon a dry surface — either glass or pa})er. The 

 behaviour was usually as follows : — The worm would curl u]) 

 closely and thrust the head under tlie body, as shown in 

 Fig. 49. The purpose of their bcliaviour seems to be to get 

 the body into as small space as possible, and especially to keep 



