MOVEMRNTS, KTC, OP FRESH-WATER PLANARIANS. 555 



concerned. There is, however, a noteworthy difference 

 between the two g-roups. In the movements of tlie hind 

 planarians the muscnlar factors (rhythmical wave motion of 

 the ventral surface, and snake-like movements of the whole 

 bod}") are more important relatively to the ciliar}' component 

 than in the fresh- water forms. In these land planarians 

 there is evidently the beginning of the characteristic 

 rhythmical wave motion of the part of the body in contact 

 with the substrate, which i-eaches its highest development in 

 the case of the MoUusca. 



II. Non- Loco motor Movements.^ 



Under non-locomotor movements will be included the 

 phenomena of contraction, expansion, " feeling movements," 

 movements of the pharynx, etc. The purpose of discussing 

 these phenomena, which are not immediately included in the 

 general standpoint, is to give an account of their mechanism 

 which may be referred to in succeeding portions of the paper. 

 These movements are the physiological foundations on which 

 the locomotor movements and the reactions are based, and it 

 is necessary to determine tlicir mechanism in order to bring 

 the analysis of the behaviour to completion. 



a. Contraction of the Body. — By the term ^^contrac- 

 tion of the body," when applied to forms like tlie flat-worm, 

 is usually meant the shortening of the body lengthwise. In 

 the flat- worm this movement is brought about by the con- 

 traction of the longitudinal muscle-fibres. It ma}' involve 

 the whole body or only a portion of it. Most frequeutly only 

 a part of the body contracts longitudinally after stinuilation ; 

 thus, if the anterior end is rather strongl}^ stinnilated in the 

 middle line, the resulting contraction will usually involve onh' 

 the anterior third of the body. In this longitudinal contrac- 



' In discussing the musculature I liave used tlirougliout, tlie nomcnciature 

 of Jijinia (loc. cit.\ in vvliose paper a very full description of this system will 

 be found. I have identified in sections of P. maculaia the followinj^ groups 

 of muscle-fibres : — {</) outer longiludinal, {d\ circular, (c) ol)lifiiie (?), {//) inner 

 longitudinal, (i°) dorso-vcniral, (/) transverse. 



