ANATOMY AND PHYSIOLOGY OF PATELLA VULGATA. 631 



On transverse section (PI. CXLIX. fig. 12) the relation of the muscle to the 

 connective tissue can be more distinctly seen. The bands of muscle underlying 

 the epithelium are observed as rounded areas, each surrounded and clasped by 

 a number of connective tissue cells. Sometimes one area only is so enclosed 

 occasionally many such are clasped by one cell, whose neucleus is seen as a 

 bulging at one point. There are a large number of trabecular composed of 

 connective tissue fibres and cells which spring from the homogeneous sub- 

 epithelial connective tissue, and passing inwards lose themselves in the general 

 feltwork of the body of the tentacle. The transverse bands of muscle are 

 specially numerous in the distal portion of the tentacle. The wrinkles are for 

 the most part temporary, but there are some where the epithelium lining the 

 valleys differs from that covering the ridges. 



Numerous very fine fibrils are seen among the connective tissue and muscle. 

 As they are highly refractile, they are probably elastic in their nature. 



A fortunate transverse section may show the epithelial cells in surface view 

 (PL CXLIX. fig. 13). They form in such an aspect a mosaic. The outlines of the 

 individual cells are roughly hexagonal or polygonal. Their ends are granular, 

 and seem embedded in a clear membrane. Probably the cuticle is a secretion 

 of the cells, and is therefore made up by a fusion of a number of distinct areas, 

 each corresponding to the end of one epithelial cell. The epithelial cells them- 

 selves are not close together. They do not touch, hence the spreading 

 appearance presented by their outer ends on longitudinal section, and their 

 isolated appearance on end view. The tactile papillae of the mantle are 

 described under the respiratory system. 



Sight. — The eye lies at the base of each tentacle, and consists of a small 

 indentation or pouch which resembles the scar of a fallen leaf. The centre of 

 the pouch is apparently filled with a black pigment. On longitudinal section 

 of the tentacle, a distinct bulge is visible in the position of the eye, with a 

 secondary bulge of lesser size below the large one (PI. CXLIX. fig. 15). The 

 large bulge forms the thick roof of a cave which is lined on its upper (roof) 

 surface by pigmented epithelium. The cave is perfectly open to the exterior, 

 and its mouth points forward. The swelling or bulge is very vacuolated, 

 there being large oval and irregular spaces amongst the connective tissue (PI. 

 CXLIX. fig. 15). The epithelium covering the bulge is continuous with the 

 epithelium covering the general tentacular surface. The cells are, however, 

 slightly longer, and are separate from each other, save near the edge of the 

 cave, where they are more crowded together. As they enter the cave they 

 increase in length, and again become wider apart. Among the long epithelial 

 cells of the outer surface of the ocular swelling are to be found a few cells 

 which spring by many processes from the basement layer, and after swelling 

 out and containing at that point a large round nucleus, terminate among the 



