23.] 



CHAPTER I. THE CELL. 95 



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different form. The two main types of cells are, first, such as are 

 spheroidal or polyhedral, with nearly equal or slightly differing 

 diameters (Fig. 46), as in pith, juicy fruits, fleshy tubers ; and 

 secondly, such as are narrow and greatly elongated (Fig. 94), as 

 n the case of fibres. 



23. The Protoplasm. The protoplasmic contents of a 

 ell present certain clearly differentiated portions. In the first 

 place there is a nucleus ; closely associated with the nucleus is a 

 body termed the centrosphere ; and finally, there are more or less 

 numerous plastids. These all lie in the general protoplasm of the 



11 which may be distinguished as the cytoplasm. 



a. The Cytoplasm is of viscid tenacious consistence, but it is not 

 a fluid. Chemical examination shows that it consists (at least, 

 when dead) of proteid substance, and apparently of a single such 

 substance termed cytoplastin ; intimately associated with this are 

 varying quantities of other organic substances, such as other 

 proteids, fats, and carbohydrates, together with water, and a 

 small proportion of inorganic ash-constituents. As it is the seat 

 of all the nutritive processes of the cell, it must obviously contain 

 at different times all the various chemical substances which enter 

 into, or are formed within the cell. 



The cytoplasm, apart from the granules of foreign matter 

 generally present in it, may be distinguished as cyto-hyaloplasm, 

 of which the delicate firmer superficial layer of the cytoplasm, 

 known as the ectoplasm, solely consists. As a rule, the cyto- 

 hyaloplasm is distinguishable into the formative cyto-hyaloplasm 

 or kinoplasm, and the nutritive cyto-hyaloplasm; the former is 

 always intimately associated with .the nucleus, and is active in the 

 processes of cell-formation ; the latter constitutes generally the 

 main bulk of the cyto-hyaloplasm. It would appear that the 

 capacity of a cell for growth and multiplication, that is, the 

 embryonic condition of the cytoplasm, must depend upon the 

 presence of a certain proportion of kiiioplasm. 



6. The Nucleus is always situated in the cytoplasm, and, in 

 actively growing cells at least, in the kinoplasm. It consists of 

 various proteid substances. Its structure, when at rest, may be 

 generally described as follows. It is bounded at the surface by a 

 membrane which belongs, however, to the cytoplasm, or, more ac- 

 curately, to the kinoplasm. It consists mainly of a semi-fluid clear 

 ground-substance, the nudeo-hyaloplasm, which, from the chemical 

 point of view, is a substance termed paralinin. In the nucleo- 



