Japanese Freslnvater Tri clads. 



Od 



ratlier strongly stinuilated, it will start at onec into a crawlin- 

 movement, which changes to gliding after a few contractions" 

 \\hen the worm starts spontaneously into movement, it n^nally 

 begins at once with the glide. When starting spontaneously, the 

 glide IS usually preceded by some of the feeling movements of the 

 head-end as in coming to rest. Among the species which 1 have 

 examined, PL vhvida is capal)le of perfoi'ming the progressive move- 

 ment With greater rapidity tlian do any others. 



The gliding movement is, so far as my observation goes 

 efïected by the action of cilia in mucus which is constantly beinc^ 

 secreted m greater or less quantity, and which gives rise to a thin 

 layer between the ventral surface of the body and the surface on 

 which the worm is moving. Immediately after heing secreted 

 into the waler this mucus is very sticky and is adherent to the 

 suhstratum. Hereby we can think of the lowest part of this mucus 

 layer, whicli is of denser consistency than its upper layers which 

 are in contact with the worm. In this upper layer, cilia cause the 

 progression of the worm body owing to their strong beatings back- 

 wards. In this case there is, of course, a very slight rhythmical 

 wavy movement of the ventral wall of the body, which assist, in 

 the locomotion. In this respect Lehnert (49) considered rliyth- 

 mical contraction waves passing along the ventral surface of' the 

 worm to ].e a factor in the movement of the freshwater planarians. 

 Pearl (oT), however, spoke of unconformation in the forms ex- 

 aimned, pointing out that some very slight muscular movement of 

 U^ ventral wall of the body, if it exists, is very insignificant. 

 Alter all, the principal factors in producing ghding I give as (]) 

 the action of cilia on the ventral surface of the bodv, {2) secretion 

 of mucus, and ('0 slight rhythmcial wavy motions of the ventral 

 wall of the body. 



Furthermore, the gliding movement takes place with the body 

 in contact with the surface film of water, wliicli serves the purpose 

 of a sohd body. This I will distinguish from the preceding by the 

 name of the so-called swimming. This movement is slower 'than 

 that on the bottom, largely on account of the greater tfexibility of 

 the surface. The surface film is of an elastic nature and does 'not 



