movemi<:nt,s, etc., of fresh-wateij planarians. 543 



reaction is one whicli would bring it towards any food 

 material which mig'ht be encountered.^ Wliile^ as will be 

 shown later, there is in the case of PI an aria a reaction 

 which is adapted to getting the organism out of danger, yet 

 it is not called forth by so weak a stimulus as is the food 

 reaction, and it is evidently for the purpose of receiving 

 stimuli of the lowest intensity that the "feeling" move- 

 ments are adapted. 



In addition to the slight "feeling movements" of the 

 head, described in the preceding paragraph, the organism 

 frequently in the course of its gliding raises the whole 

 anterior part of the body off the bottom and waves it about 

 in the water. The portion of the body so raised may in- 

 clude the wliole anterior half. The gliding is usually 

 entirely stopped or very much decreased in rate while these 

 waving movements are taking place. The head is swept 

 from one side to the other and raised high in the Avater, 

 covering a considerable area. This movement is also un- 

 doubtedly for seusory purposes. 



In the gliding movement the body back of the head is kept 

 in an approximately straight line ; that is, there is no sinuous 

 bending of the body such as is observed, for example, in 

 Stichostemma (Child, loc. cit., p. 981), or at times in the 

 movement of the earthworm. Furthermore, I have never 

 observed any regular undulation of the margins of the body 

 during movements such as take place in case of man}' poly- 

 clads, e.g., Leptoplana tremellaris (cf. Lang, '84). 

 Bardeen (loc. cit., p. 15) seems to imply that such motions 

 occur, and are an aid in the locomotion, but I am unable to 

 confirm this statement. There are, of course, slight move- 

 ments and changes of contour of the margins of the body, 

 but they are not of a prominence or character to warrant 

 thinking that they in any way contribute to the propulsion 

 of the animal. In fact, it seems more probable that they are 

 in part passive results of the motion of the whole body, and 



' A l)iief preliminary account, of t lie reactions of jMnemiopsis lias been 

 puhlislied in ' Science,' N. S., vol. xii, No. 311, pp. 927, 928, : 00. 



