86 SECONDARY DEPOSITS. 



129. Secondary deposits. In some of the cells of 

 the potato the cell wall is thickened by the deposition 

 of " secondary deposits," in which case no starch 

 granules are usually produced. This thickening 

 occurs only at certain points, leaving slight intervals, 

 through which currents of fluid continue to flow to and 

 from the bioplasm in the centre of the cavity. The pro- 

 cess may continue until the secondary deposit reaches 

 near to the centre of the cell. The channels for access of 

 nutrient fluid to the bioplasm in the centre remaining 

 open, give to the mature cell the stellate appearance 

 familiar to every one who has examined such " vege- 

 table cells." 



Just as the "secretion" in the peculiar flask-like 

 epithelial cells in the mouth of reptiles results from 

 changes in the bioplasm already described, so it may be 

 said the peculiar " contents " or "secondary deposits" 

 of other cells are "products of secretion," and that 

 they correspond to "tissue" in other cases. They 

 are all non-living substances, resulting from change 

 in bioplasm, and they constitute different kinds of 

 " formed material." The numerous pigment granules 

 in the large stellate radiating and freely communi- 

 cating pigment cells of the choroid coat of the eye, and 

 those found in various parts of the frog, afford another 

 example of a peculiar material resulting from change 

 in the bioplasm. The formation of pigment com- 

 mences at a very early period of development, and its 

 abundance seriously interferes with the investigation 

 of the structure and growth of the tissues of these 

 animals, in other respects so well adapted for the 

 purpose. 



130. Of Ciliated Cells. The cilia of ciliated cells, 

 like the outer part of the cell, the so-called cell wall, 

 are composed of formed material; but the move- 

 ments of these hair-like processes are due to changes 

 taking place in the bioplasm or living matter. The 

 vibration of the cilia ceases when the bioplasm dies, 



