OlSr THE EPII?HEAGM OP HELIX ASPEESA. 517 



Note on the Pormation of the Epiphragm of Helix as^ersa. 

 By Prof. G. J. Allman, M.D., P.E.S. 



[Read 18th June, 1896.] 



The mode of formation of the epiphragm or temporary lid by 

 which our common garden snail {ILelix aspersa) closes the 

 aperture of its shell on the approach of winter, and during the 

 continuance of hot and dry weather, does not appear to have 

 been as yet satisfactorily described. 



The epiphragm of various species of Helix forms the subject 

 of a memoir by Pischer*, who erroneously assigus its formation 

 to a secretion from the foot. Binney f has made some interesting 

 observations on its formation in Helix hortensis, and attributes 

 it to the collar or adherent mantle-margin^a conclusion which, 

 so far as it goes, is correct, but he takes no notice of any special 

 modification by which this part of the animal may become fitted 

 for the duties assigned to it. Vogt and Tung J refer to its 

 formation in Helix jpomatia ; and while they also regard it as a 

 secretion from the collar, they enter into no further anatomical 

 or physiological details. 



In ILelix aspersa the epiphragm is formed by a secretion 

 from the surface of a specially modified area of the mautle- 

 margin. It will be borne in mind that in Helix, as in other 

 terrestrial representatives of the testaceous pulmonary GTas- 

 tropods, the proper mantle possesses no free mantle skirt, but 

 is represented by the general integument of the body (pi.), 

 terminating ventrally in an even rounded and slightly thickened 

 and everted margin, which, like the rest of the mantle, except 

 where it lies over the respiratory chamber, is adnate to the 

 surface of the body. This rounded mantle-margin is the so- 

 called collar. Prom its whole extent there is developed a thin 

 glandular fold (c.^.) which is inflected over the ventral side of 

 the snail, where it forms a centrally perforated muscular disc. 

 On retraction of the animal within its shell, this can be 

 extended centripetally, so that its inner edge may reach the 

 centre, and thus completely close the aperture. It is from the 



* Paul Fischer, " De TEpiphragme et de sa formation," Journ. de Oonchylio- 

 logie, 1853, toI. iv. p. 397. 



t W. Gr. Binney, "The Terrestrial Air-breathiug Molluscs of the United 

 States," Bull. Mus. Comp. Zool. Harvard Coll., vol. iv. 1878. 



:|: Carl Vogt et Emile Yung, ' Traite d'Anatomie Compai ee pratique,' 1888, 

 vol. i. p. 772, 



