EDIBLE SNAIL. 115 



internally with the cells of the cutis which contain calcareous matter. The pig- 

 ment and calcareous glands do not extend over the surface of the foot. The 

 latter are especially numerous on the collar, and round the margins of the foot 

 in Helix. 



The body-wall consists of connective tissue and muscle-fibres. Its surface 

 in the exposed parts of the body is raised into ridges and tubercles. The muscle- 

 fibres are non-striated long cells. They occasionally appear striated, but the cause 

 of the striation is not known. The connective tissue consists of plasma-cells, a 

 matrix, and fibrils. The plasma-cells are richly developed in all Mollusca, but 

 especially in- Pulmonata where three kinds are distinguishable. These are: (i) 

 oval or round in shape with a transparent protoplasm and a round nucleus ; (2) 

 irregular cells containing refractile granules which are not fatty in nature ; and (3) 

 cells with granules of lime carbonate, which are immeasurably fine in the interstitial 

 tissue of the upper coils of the visceral dome, coarser elsewhere. These cells are 

 imbedded singly or in masses in a matrix which contains stellate cells, and connec- 

 tive tissue fibrils, the latter much more scanty than in other Mollusca. The 

 matrix is sometimes much reduced, and the first kind of plasma-cells then appears 

 to form sheaths round various organs, e. g. nerves, but the stellate cells of the 

 matrix may still be detected among them. The connective tissue membranes are 

 generally pierced by apertures, many of which are bounded by refractile rings, 

 the product of several cells which eftcircle the aperture. Glycogen has been 

 detected in the plasma-cells of the first kind both in Anodon and Helix (Blundstone, 

 P. R. S. xxxviii. 1884-85). Branched pigment-cells are found in the cutis and 

 sometimes extend inwards to its deeper layers. Changeable chromato blasts have 

 been observed by Leydig in Limax variegatus and L. (=Amafta) carinatus (A. M. A. 

 xii. 1876, p. 541). 



The buccal mass consists chiefly of an odontophore, using that term in a 

 wide sense to include the muscular and cartilaginous apparatus in connection with 

 a chitinoid (?) radula or lingual membrane bearing transverse rows of teeth. The 

 radula is developed within a radular sac and is perpetually growing throughout life. 

 The sac is essentially a ventral diverticulum of the buccal cavity, and its lining 

 cells are continuous with the oral epithelium. It is crescentic in transverse section. 

 At the blind end of the sac the lining cells are differentiated into odontoblast 

 cells, which form a transverse ridge broken up in correspondence with the number 

 of teeth present. This ridge contains in vertical section four to five large cells in 

 Pulmonata and Opisthobranchia ; a number of elongated cells in other Glossophora. 

 The singly refractile core of each tooth is secreted by these cells, the doubly 

 refractile enamel-like outer layer by the cells lying immediately dorsal to the 

 odontoblast cells, whilst the membrane or matrix uniting the bases of the teeth is 

 formed by a single cell in Pulmonata and Opisthobranchia, by several in other 

 Glossophora, placed in each case just ventral to the odontoblast cells. These 

 matrix cells split up at their free ends into fibres. The radula is carried by a 

 subradular membrane, developed by the cells of the ventral wall of the sac. The 

 membrane is borne upon cartilaginous pads, and the whole is worked by a system 

 of muscles, protractor and retractor. Other muscles flatten the radula or convert 

 it into a groove. And in some cases the subradular membrane with the radula 

 slides backwards and forwards to a limited extent over its cartilaginous supports. 



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