MOVEMRNTS, KTC, OP FRESH-WATER PI-ANARTANS. 555 



concerned. There is, however, a notewortliy difference 

 between the two groups. In tlie movements of tlie hind 

 planarians the muscular factors (rhythmical wave motion of 

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

 body) are more important relatively to the ciliary 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, Avhich reaches its highest development in 

 the case of the Molhiscn. 



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 their 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 the flat-worm, 

 is usually meant the sliortening of the body lengthwise. In 

 the flat-worm this movement is brouglit about by tlie con- 

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

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

 a part of the body contracts longitudinally after stimulation ; 

 thus, if the anterior end is rather strongly stimulated in the 

 middle line, the resulting contraction will usually involve only 

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



' III discussing I lie nius-culaluic I liave usetl tlirouiiliout, tlie iiomcnciature 

 of Jijima (loc. cit.), in wliose paper a very full (iescriptiou of this system will 

 he fouiul. I have identified in sections of V. niaculata the following groups 

 of muscle-fibres: — («) outer longitudinal, (il circular, (c) oblique (?), (d) inner 

 loiiL;itudinal, (f) dorso-veiilral, (/) transverse. 



