274 ^^^- 1'^°^- "^^l- 



the body cavity. It is somewhat smaller at its posterior end 

 than at its anterior, and ends as a blunt cone. In the living 

 worm the wall appears to be thrown up into small folds, which 

 give its outer border a wavy appearance in optical section. Be- 

 sides the green and brown food particles mentioned above, many 

 small spherical oil-globules which are very highly refractive are 

 seen scattered through the intestine. 



Stenostoma leiicops is one of the few Rhabdocoels in 

 which the intestine has a distinct muscular wall. This wall 

 is not as thick as that of the pharynx. It is made up of 

 circular and longitudinal fibres running at right angles to each 

 other. The longitudinal fibres lie next to the epithelial cells 

 lining the intestine, while the circular fibres lie next to the 

 parenchyme (Figs. 9 and 11). The circular fibres (Fig. 9, CM) 

 are circular in cross-section. They are .5 /^ in diameter. The 

 longitudinal fibres (Fig. 1 1, L.M.) are flattened bands nearly i /a 

 in width and .3 yu, in thickness. Their broadest surface lies next 

 to the circular fibres. The intestine is not connected with the 

 integument by any muscle fibres. It lies free in the body cavity, 

 and is supported only by its attachment to the pharynx, and by 

 the parenchyme surrounding it. 



The whole of the interior surface of the intestine is covered 

 with a single layer of large pear-shaped cells which are attached 

 to the muscular wall by their smaller ends, and have their long 

 axes directed radially. They are of nearly equal size over the 

 whole surface except near the valve, where they are somewhat 

 smaller. The average cells are 20 /* long and 5 /x wide at their 

 large distal ends. These cells resemble the intestinal cells of all 

 other Rhabdocoels (Graff, '82, p. 92) in being without a cell wall. 



The cells are made up of a very tenacious finely granular 

 protoplasm. Their peripheral protoplasm is clearer while their 

 central protoplasm is more coarsely granular and is arranged in 

 a fine network (Fig. 9). The large distal ends of these cells 

 are filled with vacuoles and food particles, among which are the 

 oil-globules mentioned above. The number and size of the 

 vacuoles gradually decrease toward the base of the cell. In 

 sections which have been stained with alum carmine the large 

 vacuoles at the distal ends of the cells may be seen to contain 

 many small round bodies (Fig. 9, E.) which have been stained 

 dark red or violet. 



