776 PROFESSOR J. STEPHENSON 



folding of the intestinal wall, and the lips are due to the greater height of the 

 columnar cells (fig. 3). The epithelium of the whole of the posterior part of the 

 intestine is a tall, heavily ciliated layer, presenting very numerous folds on its surface ; 

 but here again the apparent folding is due to the inequalities in the height of the 

 cells. The cells are of one kind only, with hyaline cytoplasm, and ovoid, fairly 

 large nuclei, which stain only lightly. The whole layer has a distinctive homogeneous 

 appearance, stains lightly with eosin, and cell-outlines are scarcely to be made out. 

 Near the base of the layer are frequently to be seen oval or spherical vacuoles ; these 

 from their shape are intracellular, not (as are the spaces further forwards in a some- 

 what similar position) between the bases of the cells. The vacuoles may contain 

 colourless or slightly yellow granular matter, which does not take the eosin stain 

 (hence is not of the nature of the coagulum seen in the blood-vessels and -spaces). 

 The appearance would lead one to suggest that it is an indication of intracellular 

 digestion. 



The epithelium changes its character at a short distance from the posterior end ; 

 in front of this the cells lose their thick fur-like covering of cilia and their homo- 

 geneous hyaline appearance ; they do not stain appreciably with eosin, and many 

 show a number of clear vacuoles, as if a quantity of secretion had been discharged ; 

 the lumen of the canal also becomes wider. 



Vascular System. — The peri-intestinal plexus is not conspicuous in sections, and 

 is only to be made out as a narrow chink here and there. The considerable spaces 

 between the bases of the intestinal epithelial cells, previously mentioned, belong to 

 the system, since, when, as sometimes, they contain granular matter, this stains red 

 with eosin, like the coagulum in the blood-vessels. 



The dorsal vessel passes along the left side of the intestine till it reaches segment 

 vi, or dissepiment 5/6, when it becomes dorsal. Till this point it is closely related to 

 the alimentary tube, and is invested by chloragogen cells or free chloragogen pigment. 

 The ventral vessel, which is quite separate from the intestine, is formed by the union 

 of two branches at the level of the setse of segment ii. 



Vessels are given off to the body-wall, on which they ramify, in most segments of 

 the body. They can be seen as far forwards as segment iv, and backwards nearly 

 to the posterior end. The parietal capillaries may be beautifully seen, towards the 

 anterior end of the animal, as a regular network of longitudinal and transverse 

 vessels, at right angles, marking out a series of regular rectangles on the inner side 

 of the body-wall ; the longitudinal capillaries are much closer together than the 

 transverse ; these latter are not segmental, there being more than one per segment 

 but not more than two. 



The nepJtridia are of the usual tubular and loosely coiled type, and begin in 

 segment vii. 



The cerebral ganglion is comparatively small, situated at the level of the mouth 

 aperture, in front of the pharynx. Seen laterally, it is of rounded outline, not 



