spinning Slugs and Snails. 427 



liardoncd into a llucad. One thread measured 117 cm., and 

 for the attainment of tliis len;;th over lialf an hour was 

 required. In connexion with the phenomenon in question 

 alhision is made to yet another liabit of the animals, namely 

 that of, when passinf? from one elevation to another, as, for 

 instance, from leaf to leaf, securing themselves by means of a 

 bridge of mucus, which binds the foot to the support just left 

 until tirm hold has been taken of the new one. 



In one case the same observer saw the slug crawl back on 

 the thread that had been formed, during which procedure the 

 thread was, as Ballerstedt expresses it, sucked up again by 

 the slug's mucous membrane. Further contributions on the 

 subji'ct are to be found in the ' Gartenwelt ' (vol. vii. 1903, 

 p. iUG) *, where the plienon)enon of the slug crawling back 

 on the thread is likewise noticed. The thread-drawing in 

 the case of Limax is also referred to by Leydig (' Horae 

 Zoologies,' 1902, p. 90), wiio at the same time mentions the 

 names of two earlier observers. Lister and Latham. 



Yet it is not only among the land-gastropods that this 

 singular faculty lias been shown to exist ; there are also 

 statements concerning water-mollusks. In the * Xaturwissen- 

 schattliche Wochenschrift ' (Neue Folgo, i. 1902, pp. 509 

 et seq.) \V. Brenner writes that in the case of water-snails, 

 especially Ltmncea vulgaris [= Linincea stagnalis, var. vuU 

 <707v.s], he has observed iiow the animals regulated their ascent 

 and descent through open water by means of a thread of mucus 

 attached to a point of support. An interesting note was 

 published by E. Pohl in ' Nerthus' (2. Jahrg. 1900, pp. 738 

 et seq.). It has long been known that Aplexa hjjpnorum 

 suddenly bubs up on the surface of the water and disappears 

 again equally quickly. Since Pohl appears to have found 

 out tlie explanation of this peculiar beliaviour, I should like 

 to give his statement in his own words. He writes : — 



" The snails (^Phr/sa \_Aple.ra] /typnorum) had so greatly 

 increased in number, that tiiey often hung in regular clusters 

 on the grated meat which had been thrown in. I then 

 noticed how individual snails separated from a cluster and 

 glided to the surface, in some cases straight upwards, in 

 others in an oblique direction, but alwaj's in a straight line, 

 as if uj)on some iirm object although in the middle of the 

 water. The animals also return by the same route, meet, 

 and pass close by one another. It was only after long and 

 close observation that I discovered a number of extremely 

 fine threads, that, starting from the lump of meat, led to the 



* For this rt'fereuce I am indebted to Ur. C. Brick, of Hamburg. 



