Quarterly Journal of Conchology. 401 



MOLLUSC AN THREADS. 

 A Paper 



READ BEFORE THE BIRMINGHAM NATURAL HISTORY AND 

 MICROSCOPICAL SOCIETY. 



By G. S her riff TYE. 



" So the spider spins, 

 And eke the silkworm, pattern'd by ourselves." — Hood. 



Montagu, at the beginning of this century, noticed the habit 

 in Physa fo?itinalts ot thread-spinning. He says : ^^Physafonii- 

 nalis spins a filament by which it lets itself down from the surface 

 after floating." Later, Mr. Robert Warington* gave an exceed- 

 ingly interesting account of this thread-spinning by Linmcea glu- 

 tinosa, L. stagnalis, various species of Plauorbis (not named by 

 him), and Physa fonfinalis. The latter upon one occasion formed 

 a thread so tough that he was enabled to lift the snail seven inches 

 above the surface of the water by it. The author includes in his 

 list of thread-spinners Neritina flnviatilis—oi this I shall speak 

 further on — and concludes by stating his belief that "all the fresh- 

 water snails are possessed of this power." 



Now, after this well-proven fact of spinning, stated upon the 

 authority of so good an observer, you would scarcely expect to find 

 such an observation as this : — " The Physas, especially P. kypnorum, 

 are active in habit, whether swimming foot uppermost, on the 

 surface of the water, holding themselves stationary at different 

 depths in the water, or gliding through it in sudden jerks by an 

 hydraulic action of the foot. By bringing the lateral margins of 

 this organ into contact, the animal constructs a tube for inhaling 

 and suddenly expelling Jhe water either upwards or downwards, 

 Montagu stated, and the statement has been repeated by Jeffreys, 

 that the animal spins a mucous thread for letting itself down in 



* Zoologist, 1852, pp. 3634-5 ; 1853, p, 4533. 



