188 UTRICULAR STRUCTURES. 



course its size is in inverse proportion to the thickness of 

 the layers. In many grains the cavity is reduced to a 

 minimum. These grains correspond to the cells of the 

 stony concretions of pears, and completely lignified liber- 

 cells. In other grains the cavity is of considerable size. 

 The thickness of the deposited layer of starch may be so 

 small that the starch-utricle resembles a cell with mode- 

 rately-thickened walls (fig. 15). I found such a condition 

 not unfrequently in the pith and rind of the fruit panicle 

 of Vitis. The cavity is filled with an almost colourless 

 fluid, which doubtless is no simple chemical substance, 

 but contains formative matter, such as gum, sugar, and 

 quaternary compounds, although in small quantity. 



8. General Retrospect. 



We have found various organic structures in the cell- 

 contents possessing, in all their phenomena, a great 

 resemblance to the cell itself. The general term for those 

 structures, partly on account of this similarity, partly to 

 express the actual difference, may most fitly be utricle. 



The utricle agrees with the cell* in the following 

 characters. It probably originates by the isolation of a 

 (minute] portion of organic substance, which becomes coated 

 with a membrane. Therefore from the very origin there 

 appears a distinction between contents and membrane. 

 The utricle grows both in its membrane and its contents, 

 and, in the course of this, changes its shape in manifold 

 ways. The membrane expands and becomes thickened by 

 the deposition of layers in the interior. The contents are 

 metamorphosed, and produce new organic forms. Finally, 

 the utricle propagates. 



Thus nothing occurs to the cell which is not found in 

 the utricle, at least in one or a portion of the kinds of 

 utricle. Moreover, we see that exactly the essential 

 peculiarities of the cell, the proper membrane and the 

 transformable contents, occur in all utricles. The identity 

 between cell and utricle is, therefore, tolerably manifest. 



* See the preceding Essay (on Cell-Formation). 



