ANATOMY AND PHYSIOLOGY OF PATELLA VULGATA. 623 



over the cells a delicate homogeneous highly refractile cuticle. Just before the 

 circular muscle, the cells for a short distance become spindle-shaped, and lie on 

 their sides (PL CXLIX. fig. 6). The fine processes of these cells fuse with the 

 cuticle on one side, and with the subjacent connective tissue on the other. Over 

 the circular muscle the cells are cubical and densely packed, and set directly on 

 the ends of the muscle fibres. Over them there is a tolerably distinct cuticle. 

 These cells are continuous with the epithelium of the dorsal surface of the 

 mantle. Where the pigmented epithelium is absent, as at the top of the dome, 

 there is a layer of squamous epithelium forming a superficial covering to the 

 middle layer of connective tissue. 



The second and main layer of the visceral integument consists of a feltwork 

 of connective tissue fibres and branched connective tissue corpuscles. A few 

 fibres of a more highly refractile nature may be seen which are probably elastic 

 in their nature. The middle layer is divisible into two chief layers, one of 

 which allies itself to the superficial pigmented epithelium, the other to the deep 

 pigmented epithelium when that layer exists. Each layer is composed of several 

 finer layers separable by pressure or teasing. The fibrils of which each layer is 

 made up are extremely fine, and are united by a gelatinous and in some places 

 granular matter into thin films. Connective tissue cells and nuclei are 

 scattered irregularly among the fibres. 



The third layer consists of a single layer of large cubical cells which are 

 polygonal in outline on surface view (PL CXLIX. fig. 7), and contain nucleus 

 and nucleolus, and a large number of greenish-yellow granules. These cells 

 really form the superficial layer of the right nephridium, but are usually found 

 adherent to the visceral integument when that is removed. The author has not 

 been able to make out any squamous epithelium on those parts of the inner 

 surface of the integument not covered by this pigment layer. 



The integument of the side of the foot (PL CXLIX. fig. 8) is composed of 

 cells similar to those found on the tentacle. Near the origin of the mantle the 

 cells are low columnar ; they increase in size as the lower edge is approached, 

 and on the lower half they are thrown into ridges as in the tentacle. The cells 

 are there very long, with nuclei near their centres, and with a cuticle externally. 

 The upper part of the side of the foot sometimes bears permanent ridges, 

 composed of outpushings of subepithelial tissue, covered by columnar cells, 

 much longer than those covering the side of the foot in that region. The dense 

 layer of connective tissue found beneath the epithelium in the tentacle is in this 

 situation very scanty ; and beneath it is a series of vacuoles, or lacunar spaces, 

 between the trabecular which pass from the general muscle of the foot to be 

 connected with the ends of the epithelial cells. 



The epithelium is continued round the edge of the foot for a short distance, 

 in the form of long columnar cells, which soon, however, become modified into 



