518 



PEOr. G. J. ALLMAN OK THE 



outer surface of this inflected inner collar-lobe or pTiragmato- 

 genic disc that the epiphragm is mainly formed, as a mucous 

 secretion which soon hardens into a thin membrane of horny 

 consistency, and which may increase in thickness by successive 

 deposits from the disc. 



By the contraction of the inflected disc an open space of 

 greater or less extent will be left in its centre, and through this 



Formation of the Epiphragm in Helix aspersa. 



I. Longitudinal dorso-ventral section through ventral region. 

 II. Transverse dorso-ventral section through ventral region. 

 III. Front view of aperture of shell, showing the inflected disc for the secretion 

 of the epiphragm. 



c.i. Mantle-rim. Inner collar-lobe or phragmatogenic disc. (In I. and II. with 

 the central opening expanded for the protrusion of the ventral region 

 of the snail. In III. with the central opening nearly closed.) 



CO. Mantle-i'im (" collar") on the collar-lobe. 



c.r. Respiratory chamber. 

 o. Osphradium ? 



o.r. Respiratory orifice. (In III. showing the fissure which connects the 

 orifice with the central opening.) 



2}d. Foot. 



pi. Mantle coincident with the general integument. 

 s. Margin of shell. 



The figures are diagrammatic. 



the foot and head of the snail may be protruded and again 

 entirely withdrawn. 



