:\[OVE.MI'JNTS, KTC, OF FRI'JSH-WATPIIJ PLANAlv'IAN.S. ()95 



ill the iniddlo line from in front backwards 1 have never been 

 able to obtain any definite results. Tliey simply s(|uirm 

 about in an aimless way for a mcjnu'ut when ihc eunent is 

 made and then become quiets and remain so while the current 

 passes. 'J'he direction in which tlie current is flowing makes 

 no diifereiice in their behaviour. All operated specimens 

 become very quickly paralysed by the cun-ent. 



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

 lyses planarians. Its specific effect is to cause a contraction 

 of the anode side oi- end of the body. This produces in the 

 case of fresh specimens a well defined orientation, with the 

 anterior end towards the kathode. All prog-ressive 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 Stenostoma leucops 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. Keaction to Desiccation. 



A series of experiments Avas performed to determine the 

 reactions of the aninud on drying. This is an environmental 

 condition Avhicli planarians ])robably have had to meet with 

 relative fre(|uency 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 flrst performed in the following- 

 manner : — Specimens 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 ])aper. The 

 behaviour was usually as follows : — The worm would curl up 

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

 Fig. 49. The purj)()se of their behaviour seems to be to get 

 the body into as small space as [jossible, and especially to keep 



