ANATOMY AND PHYSIOLOGY OP PATELLA VULGATA. 607 



project two smaller wings. These wings are sunk in the tissue, the triangular 

 central piece being that against which the radula works. The anterior smaller 

 wings are seen to be flaps of a collar which is formed by the turning back of 

 the plate. In other words, the anterior flaps are on a higher plane than the 

 posterior flaps. The palate is slightly depressed where the anterior margin 

 appears ; and the plate itself is curved, the concavity being ventral, and being 

 the groove in which the radula slides. Since the radula passes over the 

 anterior end of the odontophore, the teeth are therefore brought into contact 

 with the floor of the buccal cavity. There accordingly is found another plate 

 (PI. CLII. figs. 55, 56), which has not hitherto attracted the attention of de- 

 scribers of the hard parts of the limpet. It is not so large nor so distinct as 

 the other, but that it affords protection to the tissues at that point, is shown 

 by the fact that the surface of the plate is furrowed by the radular teeth. The 

 entire plate (as described below) is simply a thickened cuticle. The pharynx, 

 behind the palatal plate, becomes distinct above. It has very thin and delicate 

 walls. It may be seen to be 3-chambered, or rather to have two very evident 

 folds running clown one on either side (PI. CLIII. figs. 61, 62). The wall of 

 either lateral division has a very manifest thickening of a yellowish colour, 

 where the salivary ducts enter. The roof also of the pharynx has posteriorly 

 a large number of mucous glands in it, which give it a white appearance, as 

 contrasted with the more transparent anterior portion. 



The buccal mass now falls to be described. And, first of all, having theo- 

 retically stripped off the pharyngeal mucous membrane, the radula must be 

 noticed as distinct from the odontophore and its muscles. The radula is a 

 narrow belt usually about (in a moderately-sized limpet) y Lth of an inch broad, 

 and about twice the length of the animal in length. Anteriorly it widens out 

 into a flat plate, in the centre of which is the radula proper. The plate and 

 radula is merely a modified cuticle. The plate is bent over the front end of the 

 buccal mass. It is fastened to the mass beneath, whilst, superficially and pos- 

 teriorly, it sinks beneath the level of the muscles of the buccal mass, and runs 

 into its sheath as already described. Towards the posterior end the teeth 

 gradually disappear, and ultimately it ends in a soft hammer-shaped knob. Its 

 minute structure will be described under the histology of the alimentary system. 

 The odontophore itself is composed of muscles and cartilages. The buccal 

 mass (PI. CLIII. fig. 65), deprived of its covering and radula, is ovoid, and 

 divided almost into two hemispheres by a furrow, which runs vertically from 

 before backward. Anteriorly the furrow widens and becomes shallow, and has 

 a prominence in its centre, over which the radula was bent. Either hemisphere 

 is composed, therefore, superficially of a mass of muscle whose fibres run out- 

 wards and from before backwards, and are the muscles of the radular mem- 

 brane. Beneath these muscles lie the cartilages. The cartilages are six in 



