71 



vt'jidic'le of the lieart. Here, as in mauy utLer lamelli- 

 brauclis, we must assume that the ventricle has grown 

 up around the alimentary canal, so that the wall of the 

 heart lies betAveeu its cavit}' and the walls of the 

 alimentary canal. Outside the usual lining epithelium 

 there is a basement membrane of connective tissue with 

 a few circular muscle fibres, and external to that a thick 

 sheath of looser connective tissue. The epithelial cells 

 (fig. 44) resemble in appearance those of the ascending 

 limb of the intestine. They are deep columnar cells, the 

 height being many times the diameter, and the cilia are 

 rather poorly developed. The ends of the cells facing the 

 cavity have a strange appearance, as if either a part or the 

 whole cell were being shed into the lumen of the intestine. 

 These shed cells seem to have no stainable contents and 

 no signs of nucleus, and when cut oft' completely appear 

 in the intestine as spherical bodies faintly stained but 

 with a very definite wall. Lying scattered amidst the 

 connective tissue surrounding the intestine, especially in 

 that part passing through tlie pericardium, are 

 conspicuous wandering cells, pear-shaped, with most of 

 the protoplasm and the nucleus at the narrow end, and a 

 very large vacuole taking up practically the whole of the 

 rest of the cell. There is generally a large mass of dark 

 yellowish green material in this vacuole, which renders 

 these cells very obvious. The same cells are found in 

 considerable numbers, and carrying the same pigmented 

 contents, in the connective tissue of the digestive gland. 

 It is impossible, however, to say whether their function 

 is excretory or nutritious, and whether the coloured 

 contents are extruded by the cells lining the alimentary 

 canal or not, but they resemble so closely those of the 

 pericardial gland on the auricles, which are excretory, 

 that they are presumably the same. 



