558 RAYMOND PEAKL. 



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

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

 haps, best be taken up under the general heading of 

 ''activities," although 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 entirely, and their position is indicated only 

 by the difference in the pigmentation at that part of the 

 dorsal surface. The lateral edges of the body frequently have 



j^iG. G.— Diagram sliowing the typical appearance of a resting planarian. 

 Tlie dolAed line bounds approximately tlie area covered in tlie 

 " testing movements " wliicii precede the coming to rest (cf. text). 



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

 tion. The 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 shosvn in Fig. G. 



The coming to rest of a gliding animal is usuall}' 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 however, in most cases very considerable — usually not 

 more than two or three times its own length. It is to be 

 noted that this slower gliding which precedes the coming to 



