390 



HISTOLOGY 



are much more abundant in some parts than in others. They usually 

 are cells of about the same length as the surrounding ciliated cells al- 

 though they are by far wider owing 

 to the distended cell contents. This 

 latter consists of mucin granules 

 which fill the entire cell, packed full, 

 and gives it the round shape. 



The nucleus is crowded to the 

 cell-wall and becomes much flat- 

 tened. It lies against the wall, but 

 in this particular case it may as 

 often lie against the side wall as 

 against the bottom, where it usually 

 lies in most other mucous cells. 

 The nuclear content is very much 

 compressed. The mucous cells bear 

 no cilia, and their secretion is dis- 

 charged as a swelling mass of mu- 

 cus of thread-like form. As to the 

 periodicity of this discharge or the 

 renewal of the cells no facts were 

 observed. 



Some of these cells are so large, 

 in this and other mollusks, that they 

 cannot be contained in the epithe- 

 lium. In this case the proximal part 

 of the cell grows or pushes down and 

 lies in the connective tissue beneath 

 the epithelium. 



Many of the mucous cells of a 

 land snail, Mesodon tridentata, show 

 this specialization at its extreme, and 

 in Figure 354 one of these cells and 

 the sides of two others are pictured 

 to show their structure and relations 

 to the ordinary epithelium cells be- 

 tween which they open. As in all mucous cells, the nucleus lies flat 

 against the cell-wall and in this case against the bottom of the cell. It 

 is large and its chromatin is compacted so that its particles form an 

 almost solid mass. 



This principle is carried one step further in the nidamental cells of 

 the leech, an account of which will be found in Chapter XXII, and 

 should be glanced over in this connection. 



nu. 



FIG. 354. A deep mucous cell from the 

 mantle edge of a land snail, c.b., large 

 cell body filled with secretion; ., neck 

 through which secretion is discharging; sec., 

 secretion of this and another similar cell to 

 left; nu., nucleus; ep., surface epithelium 

 to which this cell belongs morphologically. 

 X 1000. 



