428 ^Ir. L. LinJinger on 



surface of tlie water and so rendered the tiglit-rope-walking 

 performance possible. Tlie snails remained at the surface 

 only long enough to thrust the respiratory orifice for a few 

 seconds out of tlie water, and tiien sailed back to their meal 

 again as quickly as possible. The small specimens of 

 I'UiJiorlis in the same vessel never make use of the tight- 

 rope, but crawl up the glass or let themselves float up in the 

 water without any attachment. Since I have never read 

 that Phijsa possesses the power of spinning threads, I thought 

 it advisable to mention the fact here. It is not possible for 

 the threads to be due to other creatures, such as perhaps the 

 •vvater-s))ider, since there have never been any in the vessel." 



In 1904: I myself mentioned the names of a number of slugs 

 and snails that possess the power of drawing threads *. Apart 

 from Agriolimax agrestis and Limax arborum, which are men- 

 tioned elsewhere in literature, these are among land-moUusks 

 Agriolimax Icevis, and among water-snails Ancylus Jiuviatilisj 

 Aj'ltxa hyp7iorum, Bi/thiitia tentaculafa, Pliysa fontinalis, 

 and a species determined by me as Fhysa acuta f. 



To-day I am able to add to the list Limax variegatus, 

 Amphipeplea glutinosa, Planorbis carinatus, P. complanatus^ 

 P. nitidusj and P. umhilicatus. 



As regards the thread-spinning in the case of the species 

 of A gi-iolimax and Limax, I cannot add much that is new to 

 Ballerstedt^s description. While it is but seldom that this 

 kind of locomotion, which at first sight seems somewhat 

 strange as exhibited by slugs, can be witnessed in the open — 

 for which the observer ratiier tlian the slugs is responsible — 

 it can be produced experimentally at any time. In order to 

 obtain a successful result it is necessary that too great a 

 distance should not at first be interposed between the animal 

 and the point that it has to reach. An interval of about 

 15 cm. is sufficient. Once it has formed a piece of thread, 

 the distance is generally immaterial. For the actual experi- 

 ment the animal is placed upon a portion of a leaf suspended 

 by a fine thread. 



Crawling back on the thread already drawn out is also 

 nut uncommon, with the reservation, however, that well- 



• " Verzeichnis der in und um Erlangen beobachteten Molluskeu," 

 Abh, Naturhist. Ges. Niirnberg, Bd. xv. 2. Heft, p. 68. 



t As Hen- D. Geyer, of Slutlgart, informed me, this is probably not 

 Physa acuta, but a similar species introduced from North America. The 

 same remark very likely also applies to the species recorded as Phijm 

 acuta by O. Goldfuss (' Die Binueumollusken Mitteldeutschlands,' 1900, 

 p. 28) for Leipzig, and by H. Sell (Nachrichtsbl. deutsch. mal. Ges. 

 Ijd. xxxvii. 1905, p. 40) for Copenhagen. 





