KEW : ON THE MUCUS-TIIUEADS OF LAND-SLUGS. I59 



spin best when hungry and in search of food ; but the faculty is facih- 

 tated, I imagine, more by the greater consistency acquired by the sUme 

 during captivity than by reduction of weight or other circumstances 

 attending abstinence. 



As regards the length of thread a slug is able to produce, it may be 

 recalled that the thread of the small slug observed by Shaw (3) appears 

 to have been nearly eight feet long, and even this is probably exceeded 

 by threads oi Agrioliinax agrestis} seen by D.T. (33), the latter serv- 

 ing, apparently, for safe descents of nine feet. Threads three to seven 

 feet long have been recorded by Hoy (2), Latham (4), Reeve (22), 

 Harte (23), Eimer (30), Warner (35), Ward (36), W.R. (45), Foreman 

 (47), and Crovvther (50). The writer has seen a thread thirty-seven 

 inches long spun by young Arion sub/uscus, and one thirty-nine inches 

 long by Agrioliinax agrestis. The creatures cannot often be induced 

 to make threads many times on the same day, for they usually become 

 reckless and fall without threads after a few trials ; a remarkable series 

 of performances, however, is recorded by Latham (4) of Agr. agrestis, 

 which, placed on a window-frame, made a thread two feet long, and 

 on being replaced made in succession four others, each apparently of 

 a length of nearly four feet. 



The speed of the descent is a little ditHcult to observe : L. maximus 

 watched by Reeve (22) appears to have descended, rather rapidly, eight 

 to nine inches per minute ; Mr. Standen, moreover, has remarked to me 

 on the " rapidity with which L. arboruiii slips down by its thread'' ; 

 on the other hand, the slug seen by Hoy (2) was approaching the earth 

 very slowly at the rate of an inch in about three minutes. I have not 

 seen a range so great as that here indicated. Montagu (4) " observ- 

 ing by his watch " found that Agr. agrestis descended at the rate of 

 3^ inches per minute, and this, I think, is about the rate at which the 

 thread is usually lengthened. An Agr. kevis observed by me made 

 two to three feet of thread at about three inches per minute ; the 

 quickest spinning I have seen was that of Agr. ag?-estis, which made 

 in two minutes about ten inches of thread, and the slowest that of 

 Ajiialia sowerbyi, which spent five minutes in spinning six inches. 



It is stated by Binney (20) that the creatures sometimes pause in 

 their descent and remain in mid-air for a time, but this does not agree 

 with the writer's experience. Nearly all my slugs descended gradually 

 till they fell or reached a support ; it is true, however, that slight 

 pauses were occasionally observed. 



While the animals are descending the locomotory muscles of the 

 foot are in constant motion, and during the whole process one can see 

 little wave-like appearances gliding from the tail forwards along 

 the whole length of the foot. This appearance is the result of 

 muscular action identical with that of the animal's ordinary crawling 



