C06 



TONGUES OF GASTEROPODS. 



however, from the examination of the surfaces presented by fracture. 

 The Membranous residua left after the Decalcification of the shell by 

 dilute acid, may be mounted in weak Spirit or in Goadby's solution. 

 471. Tongue of Gasteropod Mollu&ks. - The organ which is com- 

 monly known under this designation is one of a very singular 

 nature ; and we should be altogether wrong in conceiving of it as 

 having any likeness to that on which our ordinary ideas of such an 

 organ are founded. For instead of being a projecting body lying 

 in the cavity of the mouth, it is a tube that passes backwards and 

 downwards beneath the mouth ; its hinder end being closed, whilst 

 in front it opens obliquely upon the floor of the mouth, being (as 

 it were) slit-up and spread-out so as to form a nearly flat surface. 



On the interior 

 Fig. 317. of the tube, as 



well as on the flat 

 expansion of it, 

 we find numerous 

 transverse rows 

 of minute Teeth, 

 which are set 

 upon flattened 

 plates; each prin- 

 cipal tooth some- 

 times having a 

 basal plate of its 

 own, whilst in 

 other instances 

 one plate carries 

 several teeth. — 

 Of the former 

 aiTangement we 

 have an example 

 in the 'Tongue' 

 of many Terres- 

 trial Gasteropods, 

 such as the Snail 

 {Helix) and Slug 

 ( L im ax), in which 

 the number of 

 plates in each row 

 is very consider- 

 able (Figs. 317, 

 318), amounting 

 to 180 in the 

 large garden Slug 

 (Limax maxi- 

 mus) ; whilst the 

 latter prevails in 



Portion of the left half of the Tongue of Helix 

 hortensis ; the rows of Teeth near the edge separated 

 from each other to show their form. 



Fig. 318. 



Tongue of Zonites cellarius. 



