l62 JOURNAL OF CONCHOLOGV, VOL. ID, NO. 6, APRIL, 1902. 



weighs ten to seventeen grains, and much heavier slugs can suspend 

 themseh'es. It is true that the animals often fall, but as far as the 

 writer's experience goes, the thread when once set never breaks, the 

 fall being due either to a temporary failure in the slime-supply or to 

 the rupture of the film while collapsing. It is possible by taking hold 

 of the thread to lift the animal by it; this has been done by the writer; 

 and Montagu (4) thus carried Agriolimax to a distant room. Saunders 

 (19) found the thread capable of supporting a weight greater than that 

 of the slug ; he found also that it \yas somewhat elastic. The latter 

 character is frequently apparent when the animal falls, the thread often 

 springing back, curling up, and contracting considerably. According 

 to a note communicated by Mr. Crawshay, a thread thirty inches long 

 " contracted like elastic to nineteen inches, and dried in the air like a 

 silk-thread." If the animal falls early in its descent, before the thread 

 has had time to dry, a small speck of slime is all that remains ; threads 

 of longer descents, however, have considerable permanence, and may 

 be kept in boxes or between pieces of glass for years. When a new 

 support is reached the thread, though it usually springs up as just 

 described, occasionally remains attached at both extremities — this I 

 have observed in Avion circumscriptns; and Mr. Standen states that he 

 found, one morning at Oban, a thread stretching from the edge of a 

 table to the floor, marking the aerial course of L. arborum, which had 

 escaped from a box during the night. While the animals are suspended 

 there is no difficulty in taking lengths of thread on slips of glass, and 

 Mr. M. F. AA'oodward has obligingly examined with the microscope 

 specimens thus obtained of threads of Agr. agrestis. A somewhat 

 fibrous appearance is presented, but this, it is supposed, is merely clue 

 to inequality resulting from the folding and giving-way in places of the 

 film as it collapses ; cell-like bodies are observable, but do not seem 

 to form an essential part of the thread. 



Besides the use of the thread for descent, the animals can also em- 

 ploy it, if they do not find a support or fall, as a means of ascent to 

 their former position. This most unlooked-for fact, perhaps the most 

 extraordinary yet recorded of the slugs, was first noticed by Saunders 

 (19) ; it has been observed also by Harte (23, 26), Zykoff (41), and 

 W.R. (45). The slug observed by Saunders turned after descending 

 eighteen inches. Harte several times saw Agr. agrestis stop, after a 

 few inches, and commence an ascent, and some by this means re- 

 gained the branches from which they had suspended themselves ; on 

 one occasion this observer had four individuals suspended at the same 

 time, and of these three returned a distance of five inches and one of 

 two inches, and all regained the branch in safety. The observations of 

 W.R. also relate, probabl)', to Agr. agrestis; and Professor Eimer 

 informs me that since the publication of his paper (30) he has seen 



