CALCIFEROUS GLANDS 31 



Many organs that have high metaboHc rates and that are 

 associated with a secretory or absorptive function, e.g. the distal 

 tubules of mammalian kidney and the planarian nephridium 

 (Danielli and Pantin, 1950), contain considerable quantities of 

 alkaline phosphatase. This enzyme has been demonstrated by 

 histochemical methods in the calciferous glands (Bevelander and 

 Nakahara, 1959). It is associated with mitochondria and is 

 localized at the borders of the cells, the amount present increasing 

 as cellular activity rises, and decreasing as the cell passes into a 

 quiescent phase. 



Many mitochondria, of varying types, are found in the cells of 

 the glands (Myot, 1957; Guardabassi, 1957) and electron micro- 

 scope studies have confirmed the identity of these structures 

 (van Gansen, van der Meersche and Castiaux, 1959). 



Two types of cell, however, have been described by van Gansen 

 (1959a) who has provided the most recent work on the glands. This 

 author shows that the glands can be divided into two regions, 

 depending upon the cell type. The posterior portion of the 

 gland, at which the blood arrives directly from the intestine, is 

 composed of cells containing many ''batonnets" and several types 

 of mitochondria. In the anterior portion of the glands the cells 

 contain large amorphous concretions of calcium carbonate, these 

 not being found in the rear sections. Alkaline phosphatase occurs 

 in both regions, but has different distributions, even in contiguous 

 areas. A small mucus secreting area is present where the glands 

 pour their contents into the gut (Figs. 10 and 11). 



The "batonnets" of the rearward cells are thought to be 

 infoldings of the cytomembrane of the cells, bearing a close 

 resemblance to the cells of the proximal tubule in mammals 

 (Sjostrand and Rhodin, 1953). The edges of the cells bordering the 

 lumen of the gland are ciliated and bear small outgrowths remini- 

 scent of a brush border. Cordier (1934) described a very similar 

 series of structures in the wide tube of the nephridium, and 

 Ramsay (1949b) has since shown that this area is the seat of 

 formation of the hypotonic urine excreted by the earthworm, a 

 process probably involving re-absorption of water and salts through 

 the nephridial wall. 



Using the similarity in structure of the calciferous cells and those 

 of kidney, nephridial tubules and other actively resorbing systems 



