310 Kew: Slime -Threads of Planarian- Worms. 



much attenuated, its body attaining- the extraordinary length of 

 14 inches. Dr. Scharff, more fortunate, observed a specimen 

 from a greenhouse at StrafTan, Co. Kildare, descend by a thread 

 which did not break until it was 8 inches in length ;* and 

 Mr. Lehnert, who had 12 specimens of this planarian from 

 Leipzig-, Berlin, Kew, etc., saw the creatures hang by threads of 

 equal or greater length. The last-named naturalist, who made 

 numerous observations, recognises that the thread is identical 

 with the slime-trail of ordinary progression, and that, though it 

 appears to be drawn from the posterior extremity of the animal, 

 this is not really the case, for the creature when in the air is 

 creeping by means of its cilia upon the locomotory mucus which 

 it emits from the creeping-sole, and this mucus, when left by the 

 posterior extremity of the animal, forms the thread., The animal, 

 Lehnert says, gradually crawls from its support, the free anterior 

 portion, in the meantime, executing various movements ; finally, 

 the posterior extremity passes from the support, and the animal 

 hangs in the air by a thread continued -from the slime-film left 

 upon the support. The suspended animal, sometimes holding 

 its body exactly as though it were crawling upon a solid surface, 

 sometimes swings and turns, and curves its anterior part in 

 various directions. The thread, the slime for which the sole 

 continues to secrete, is gradually lengthened, and it may sustain 

 the descending, free-hanging animal till the length of the thread 

 about equals the length of the animal's body. If the creature 

 has not by this time encountered a new support, the thread 

 usually gives way, and the animal drops. If, on the other hand, 

 a new support has been found, the thread persists, and the 

 animal, still sustained by it posteriorly, crawls with its anterior 

 part upon the new support, and the rest of the body follows 

 gradually, the hinder portion descending vertically along the 

 thread-forming mucus until the whole of the animal has occupied 

 the new support. The thread, the stress upon which is 

 gradually relieved as the new support is occupied, may thus 

 attain a length about twice that of the animal's body — the 

 creature being capable, it will have been gathered, of descending 

 in safety from one object to another two lengths distant. 

 Usually, though not always, the thread breaks off. when the 

 posterior extremity reaches the support ; and, thus liberated, it 

 contracts irregularly. During the descent the animal sometimes 

 becomes more or less twisted ; and in this case, as it crawls 



* Scharff, Irish Naturalist, III. (1894), p. 242, 



Naturalist,. 



