522 J^AYMOND PEARL. 



goiiocepliala to light. This form moves away fconi the 

 source of the light. The amount of directive influence was 

 moasurecl. It was found that specimens without eyes, i.e. 

 in which the anterior end had been cut off, react in much the 

 same way to light as do normal individuals, ''^ in that they 

 have a tendency to turn away from the course when directed 

 towards the source of light, and to keep in it when directed 

 a,wn.y from the source, though with less precision, and often 

 to less extent, than planarians with eyes." Furthermore, 

 figures are given showing that planarians fi-om which the 

 antei'ior end has been cut off move more slowly than normal 

 animals. This is thought to be due to the absence of the 

 eyes. 



The most extensive paper dealing with the physiology of 

 planarians is that of Bardeen (:01). This paper is mainly 

 devoted to a study of regeneration in PI an aria maculatn, 

 but before entering upon the discussion of this subject the 

 author devotes considerable space to an account of the 

 anatoni}^ and physiology of the organism. In the section 

 devoted to physiology, the author discusses, under the 

 caption " Environmental Activities," sensation, movement, 

 and the central nervous system. The author makes the 

 remarkable, and obviously incorrect, statement that the 

 planarian is sensitive only to light and contact. A ver}' few 

 inconclusive experiments having reference to thigmotaxis, 

 geotaxis (?) and hydrotaxis, are reported. The statement is 

 made that specimens '' would remain unmoved by the presence 

 close by their side of a piece of fresh snail, a food much 

 prized by them." Two forms of movement are described — 

 "swimming" and crawling. The author's description of 

 what he calls the " swimming " movement will be discussed 

 later in this paper. ]3rief and vei'y general statements 

 regarding the reactions to mechanical stimuli are presented. 

 Under the heading '' Internal activities " are discussed 

 deglutition, food dispersion, defecation, and respiration, in a 

 rather loose and hypothetical way. The author makes the 

 following contribntion regarding excretion in Planaria: — 



