STRUCTURAL BASIS OF THE HUMAN BODY. 



13 



Indirect cell division. In certain and numerous cases the division of 

 cells does not take place by the simple constriction of their nuclei and 

 surrounding protoplasm into two parts as above described (direct division), 

 but is preceded by complicated changes in their nuclei (karyokinesis). 



FIG. 6. Diagram of a cartilage cell undergoing fission within its capsule. The process of divi- 

 sion is represented as commencing in the nucleolus, extending to the nucleus, and at length involving 

 the body of the cell. (Frey.) 



These changes consist in a gradual re-arrangement of the intranuclear net- 

 work of each nucleus, until two nuclei are formed similar in all respects 

 to the original one. The nucleus in a resting condition, i.e., before any 

 changes preceding division occur, consists of a very close meshwork of 

 fibrils, which stain deeply in carmine, imbedded in protoplasm, which 

 does not possess this property, the whole nucleus being contained in an 

 envelope. The first change consists of a slight enlargement, the disap- 

 pearance of the envelope, and the increased definition and thickness of 



FIG. ?. Karyokinesis. A, ordinary nucleus of a columnar epithelial cell: B, c, the same nucleus in 

 the stage of convolution; D, the wreath or rosette form; E, the aster or single star: F, a nuclear spin- 

 dle from the Descemet's endothelium of the frog's cornea: G, H, i, diaster; K, two daughter nuclei. 

 (Klein.) 



the nuclear fibrils, which are also more separated than they were and stain 

 better. This is the stage of convolution (Fig. 7, B, c). The next step in 

 the process is the arrangement of the fibrils into some definite figure by 

 an alternate looping in and out around a central space, by which means 



