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possess no cell-wall ;— it is derived from the protoplasm by a 

 process of change. Of its more minute structure and properties 

 I shall presently have to speak. 



The protoplasm, or living and essential constituent of the 

 structural element or cell, is at first clear, and transparent; 

 often, however, we find that it is more or less opaque, exhibiting 

 a turbid whitish granular appearance; the granules which render 

 it so being due to the presence of drops of oil, granules of starch, 

 or granules of inorganic salts. The layer of protoplasm, 

 which lines every portion of the cell-wall, is not uniformly 

 granular throughout, for between the granular portion and the 

 cell-wall there is a clear space, and the protoplasm here is 

 transparent, hyaline, and harder than the inner portion. Con- 

 sequently there is a division of the protoplasm into two distinct 

 portions — a granular portion or endoplasm, and a hyaline 

 portion or ectoplasm. The ectoplasm is comparatively inactive 

 in the performance of the chemical processes which go on in 

 the cell ; it is protective of the inner active region, and hence 

 probably its clearness is due to the fact that no foreign bodies 

 are needed there. This differentiation of the protoplasm into 

 two also occurs in organisms which are destitute of a cell-wall. 

 In the centre of the mass of protoplasm is a body with a well- 

 defined outline of a darker colour than the protoplasm, and in 

 some cases appearing to be merely slung in certain bridles of it, 

 (as in the cells of the filaments of Tradescantia) ; this body is 

 nothing but condensed protoplasm, and is called the nucleus. 

 Nuclei have of late been detected by a German observer in the 

 cells of the Fungi, and of the lower Algae, where they were for 

 a long time supposed to be absent, and here they are not single, 

 but in great numbers, so that if these observations be trust- 

 worthy, we do not know of any vegetable cell which does not 

 at some period possess a nucleus. The function of the nucleus 

 is to act as a governor or director of the protoplasm of the cell, 

 and hence it presides over division, and is usually the first 

 portion of the cell to divide. As the cell increases in age, 

 minute clear spaces called vacuolae make their appearance in 

 the protoplasm ; these are filled with a watery fluid known as 



