Keiv: Slime -Threads of Planarian -Worms. 315 



fall or let themselves down by their threads to the bottom.* Of 

 the little freshwater Mesostoma rostratum,\ Dalyell notes that its 

 adhesive faculty is so slight that the containing- vessel can scarce 

 be touched without the consequent cessation of the animal's 

 hold ; the same, he adds, is a leading- characteristic of other 

 planarians, though in an inferior degree ; ' they suddenly 

 abandon the plane of position, and drop through the water, 

 with contortions of the body, as if to break their fall, while 

 they are evidently aided by a filament invisible to the naked 

 eye.' } For larger species of this genus, M. ehrenbergii and 

 M. tetragomim (the former ^ inch or more long), we have 

 observations by Professor Schneider, who states that the 

 creatures attach a slime-thread to floating Duckweed (Lemna), 

 and suspend themselves from it head downwards ; and it some- 

 times happens that whole companies of them are seen in this 

 position. § Dalyell says that M. rostratum, possessed of extra- 

 ordinary activity, swiftly traverses the substances surrounding 

 it, with its snout-like anterior extremity incessantly in motion 

 as if in search of prey || ; and in some of the books we find, for 

 M. ehrenbergii, etc., the surprising statement that the creatures 

 'ensnare their prey by means of slimy threads.' The state- 

 ment arises, no doubt, from observations by Schneider, who 

 remarks of the two species referred to by him that they use 

 their slime in a murderous manner for the capture of prey — 

 small worms, Entomostraca, mites, larvae of Notonecta, etc. 

 The Entomostraca are preferred to anything else, and when one 

 of them approaches, the Mesostoma gives it a slight blow with 

 the anterior extremity, whereupon the victim becomes covered 

 with slime and is unable to get away ; large numbers of these 

 little creatures, moreover, become entangled in the slime which 

 the Mesostomas leave about the vessels in which they are kept. 

 The capture of comparatively large prey, such as larvae of 

 Notonecta, is a less easy task ; and Schneider affirms that the 

 Mesostomas catch these creatures in nets which they spin at 

 the surface and through the water ; if there are no larvae in 



* Jensen, Turbellarier ved Xorgvs Vestkyst, 1878, p. 68; L. v. Graff, 

 Monographic der Turbellarien : I. Rhabdocoelida, 1882. p. 424. 



t Planaria velox. 



£ Dalyell, 1814, op. cit., p. [31. 



>; Schneider, Untersuchungen iiber Plat helmint hen, 1S73, pp. 23*5. 



|! Dalyell, 18 14, op. cit., pp. 130-1. 



** Royal Natural History, VI. (1896), p. 469. 



1900 Oct oho r 1. 



