558 



KAYMOND PEARL. 



portion of the life of a plauarian is spent in a condition of 

 rest, it will be well to discuss this matter ; and it may, per- 

 haps, best be taken up under the general lieading of 

 "activities," althongh really the opposite of activity. 



The appearance of the worm when resting is, as has already 

 been mentioned, quite different from its appearance in the 

 active condition. The body is shorter, wider, and thicker. 

 The ordinary contour of the head is almost entirely lost, and 

 in place of the sharply pointed anterior end of a form like P. 

 dorotocephala, the end is evenly rounded. The auricles 

 disappear almost entirel}'', and their position is indicated only 

 by the difference in the pigmentation at that part of the 

 dorsnl surface. The lateral edges of the body frequently have 



Fig. G.— Diagram showing the typical appearance of a resting planarian. 

 Tlic dotted line bounds approximately the area covered in the 

 " testing movements " which precede tlie coming to rest (cf. text). 



a wavy line instead of the straight one of the active condi- 

 tion. 'V\\c anterior end of the body is in contact with the 

 bottom, and not raised as in movement. The general appear- 

 ance of a resting planarian is shown in Fig. G. 



The coming to rest oF a gliding animal is usually done in a 

 very characteristic way. First, the animal glides more and 

 more slowly for some distance before reaching the point at 

 which it will finally stop. The distance before reaching the 

 stopping place in which the worm glides appreciably slower 

 is not, iiowever, in most cases very considerable — usually not 

 more than two or three tim(>s its own length. It is to be 

 noted that this sU)wer gliding which p)'ecedes the coming to 



