520 KAYMOND PEAKL. 



stances uut {ictually in contact with it. This point will be 

 discussed in detail later. 



Lillie (:01) brings out the fact that cut posterior parts of 

 the body of Dendrococlnni lacteum show very little 

 movement, and in general fail to give the typical reaction to 

 lio-ht after removal of the brain. 



Finally, there are accounts of the natural history and 

 habits of various planarians in numerous ''natural histories" 

 and text-books. As such accounts are for the most part 

 brief and of no great significance from our standpoint, they 

 will not be referred to in detail. 



II. Physiological. 



The literature dealing with the planarians fruuj a purely 

 ])hysioh)gical standpoint is very meagre. Furthermore, for 

 the most part it deals only with special phases of the 

 physiology of these organisms, there being very little work 

 attempting to bring the behaviour of planarians into relation 

 with that of other forms. 



The most important work dealing experimentally with the 

 physiology of the movements of ilatwornis which I have 

 found is that of Loeb ('91). The purpose of his work was to 

 determine in how far the reactions of such low organisms as 

 worms were dependent upon the brain. The planarians used 

 were Thy sano zoo n brocchii, and Planaria torva. In 

 Thysanozoon he found that if the animal were (piickly cut 

 into two pieces transversely with a sharp scalpel or scissors 

 the anterior piece crawled on undisturbed, while the 

 posterior piece showed no further movement. The conclu- 

 sion is then drawn that "Die Spoutaneitat der Progressiv- 

 bewegungen ist also bei Thysanozoon eine Fuuktiou des 

 Gehirus." This form shows no definite '' geotropic " reac- 

 tion, but crawls about with the axes of the body forming any 

 angles with the direction of gravitation. The very strong 

 " stereotropism " (thigmotaxis) of the ventral side of Thy- 

 sanozoon, which always tends to keej) in contact with a 

 solid body, is noted. This reaction is found to be inde- 



