FORMED MA TERIAL. 5 1 



the loss of those old cells which are gradually removed 

 from the surface.* Each mass of germinal matter increases 

 in size by the absorption of nutrient pabulum, which, as 

 in all other cases, passes through the layer of formed 

 ' material. But at the same time, a portion of the germinal 

 matter undergoes conversion into formed material, which 

 accumulates upon the surface within that already formed, 

 and as each new layer is deposited upon the surface of the 

 germinal matter, those layers of formed material already pro- 

 duced are stretched, and with them the last developed are 

 more or less incorporated. (PI. VIII, fig. 28, p. 60.) For a 

 time, the germinal matter increases, while new-formed 

 material is being produced. In other words, both the 

 constituent parts of the entire cell increase in amount 

 up to a certain period of its life. (PI. IV, b.) But as 

 new cells continue to be produced below, those already 

 formed are gradually removed farther and farther from 

 the vascular surface, while at the same time their formed 

 material becomes more condensed and less permeable to 

 nutrient matter. From this point, each entire cell ceases 

 to increase in size, while the germinal matter actually 

 diminishes, because it undergoes conversion into formed 

 material ; at the same time, owing to the increased density 

 of the formed material, and its greater distance from the 

 vessels, little new pabulum is taken up to compensate for this. 



* The description here given is not strictly accurate, inasmuch as 

 the new masses of germinal matter do not all move in a direction to- 

 wards the surface. Some tend in the opposite direction, towards the 

 subcuticular tissue, but this need not be discussed here, as it would 

 complicate the description without helping in any way to elucidate the 

 question now being considered. 



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