117 



cavity of the duet. The opening to the exterior is lined 

 for a short distance with non-glandular, more compact, 

 normal ciliated epithelium, the lips being formed bj' a 

 slight development of cushions of connective tissue. 



In addition to the organ of Bojanus, excretion is 

 carried on by the pericardial glands. These are contined 

 to the auricles, to which they give a very distinct brown 

 tint. T'he auricle has the wall thrown into numerous 

 pockets, which increase its surface. It is formed of a 

 single layer of epithelial cells (fig. -49, Aur.), somewhat 

 flattened, and with prominent nuclei. Internal to this, 

 there is a considerable amount of loose connective tissue 

 with scattered muscle fibres, and amidst these lie the cells 

 (Aur. ex.) w^hich by reason of their contents give the 

 brown colour to the surface. They are large, and very 

 similar in form to those described in the connective tissue 

 sheath of the alimentary canal, except that more proto- 

 plasm appears to be present; oval in shape, with the 

 nucleus near one end, and the rest of the cell almost filled 

 by a mass of some refractive structureless substance 

 surrounded by a thin cortex of protoplasm. Usually, the 

 large mass of cell contents shows a granular central 

 portion of an olive green tint, and surrounding this a 

 part which stains, like connective tissue and chitin, a 

 light blue with Methyl-blue-eosin. 



The two forms of excretory organs already described 

 seem to perform different work. If indigo carmine 

 solution is injected into the animal, it will be eliminated 

 by the cells of the organs of Bojanus ; whilst if ammonium 

 carminate is injected, it is taken up by the pericardial 

 excretory cells. 



The latter cells, which have been described as placed 

 chiefly on the auricles, occur also in the mantle, the 

 visceral mass and around the intestine. 



