CHAPTER X. 

 CELL DIVISION: DEVELOPMENT OF GERM-CELLS. 



THE great majority of cells possess the faculty of division. 

 The division by simple fission of the nucleus and cytoplasm 

 (Direct Division) is a rare mode. The most general method 

 is one of much greater complexity, and is accompanied by the 

 formation of threads in the nucleus, and by movements of 

 those threads (Indirect Division). Hence the division of most 

 cells is known as mitosis or karyokinesis, in allusion to the 

 nuclear thread and nuclear movements that accompany the 

 process. 



Before the process of indirect division can be understood it 

 is necessary to explain certain details of cell-structure. Every 

 cell consists of a corpuscle of protoplasm differentiated into 

 two substances one nuclear, the other cytoplasmic. The 

 nuclear substance is generally in the form of a definite body, 

 the nucleus, which is imbedded in the surrounding cytoplasm. 

 The nucleus is not uniform in structure, but exhibits- a spongy 

 character and consists of a substance called linin, and holds a 

 viscous nucleoplasm in its meshes. These substances, the 

 linin and the nuclear sap or nucleoplasm, do not stain with 

 logwood dyes, hence they are called the achromatic elements 

 of the nucleus. The linin network is, however, concealed by a 

 closely applied covering of granules, thickened here and there 

 at the nodes or knots, and this covering stains strongly with 

 most dyes, and hence is called chi-omatin. When the knots 

 of this chromatic network are very marked they are called 

 nucleoli, but there are also one or more spherical bodies lying 

 in the nuclear sap, and these also are called nucleoli. 



When a cell is about to divide, and throughout life in 



