ANATOMY AND PHYSIOLOGY OF PATELLA VULGATA. 611 



lined by cubical epithelium. Both tubules and ducts are supported by a base- 

 ment layer of connective tissue. The ducts enter the pharynx towards its 

 anterior end, and where they do so there is a large mucous gland, the cells of 

 which, however, are largely supplied with the yellow granules found in the 

 salivary glands. The pharynx is a very complicated structure, and its fuller 

 investigation is left to the physiological part of this research. In the anterior 

 part there are two distinct folds from the dorsal wall ; the lateral chambers 

 are continued into a pouch over either shoulder. These folds, along with others 

 on the ventral wall, are continued into the crop. The entire pharynx is lined 

 with columnar epithelium. 



The crop is thick-walled, but in reality the thickness is due to the presence 

 of an enormous number of long compound tubular follicles, much resembling 

 those found in the large intestine of a mammal. There are two very distinct 

 longitudinal folds running from one end of the crop to the other on the ventral 

 wall, and also one pretty definite fold on the dorsal surface. Each of these 

 folds has secondary longitudinal folds on itself. Further, the wall generally is 

 thrown into transverse folds, which are arranged like a series of leaflets across 

 the intervening spaces. On these folds are developed the follicles above- 

 mentioned. The follicles are lined by elongated cubical or columnar cells, two 

 or three layers deep. The superficial layer is composed of pear-shaped cells, 

 which are filled with granular protoplasm. The larger cells contain rounded 

 granular masses of a highly refractile nature. These masses are often placed in 

 a vacuole, and are apparently shed into the lumen of the follicle. The cells 

 spring from a basement membrane of connective tissue cells, and there is a 

 lymph space between every two follicles. These spaces communicate with the 

 spaces in the connective tissue surrounding the glandular stomach, and con- 

 sequently with the circulatory system. 



The liver, as already stated, is a compound saccular gland, irregular in 

 form, and filling up generally the spaces between the glandular stomach, the 

 true stomach, and the various coils of intestine. It consists of a framework of 

 connective tissue, covered by secreting epithelium. The epithelium is one 

 layer deep, and is extremely difficult to make out, so full is the whole tissue of 

 biliary secretion. When the debris is washed away, usually the epithelium is 

 also removed. When found, it is seen to be composed of delicate columnar 

 or cubical cells, without evident cell wall, and filled with the minute droplets 

 or granules of which the biliary secretion is composed. The cells are not 

 unlike goblet cells in form. There are usually to be seen some minute cells 

 between the bases of these larger cells, which probably replace the larger cells 

 when destroyed. The bile is apparently poured into the glandular stomach by 

 a number of ducts. A fortunate section may show the opening of one of 

 these ducts (PI. CL1II. fig. 71). The ducts open between the bases of the two 



