finds this state referred to as the resting stage. Since there is reason to 

 believe that this stage is far from "resting" in the physiological sense, 

 but rather that it is the most active period, the term "energic phase" 

 may serve the purpose better (Berril and Huskins, 1936). Nonetheless, 

 the terms "interphase" and "interkinesis" are widely used to designate 

 the stage between two successive nuclear divisions and, in this restricted 

 sense, seem quite adequate even though some other term would appear 

 more suitable for nuclei of differentiated cells. 



Figure 5-1. Diagrammatic Representation of the Stages of Mitosis: (a) 

 prophase; (b) metaphase; (c) anaphase; and (d) telophase. (From Wilson, 

 G. B., 1952. "Outline of Genetics," Michigan State University Press, East 

 Lansing, Mich., Fig. 2, p. 6.) 



The nucleus at this stage is as described in Chapter 4. The chromo- 

 somes lie in the form of more or less loosely coiled threads, usually 

 somewhat closely appressed to the membrane. Most cytologists consider 

 them to be already duplicated, and some workers believe them to be 

 multipartite. They may or may not stain intensely with standard nuclear 

 stains at this stage, presumably depending on the distribution of nucleo- 

 protein which appears to vary with the species. Nucleoli and Feulgen- 

 positive chromocenters are also conspicuous during this stage. 



Prophase 



At the beginning of division the chromosomes start to contract, 

 thicken, and undo their coiling. Part of this change appears to be asso- 

 ciated with the development, at right angles to the old coil, of a new 

 one which grows from a coil of many small gyres to one of relatively 

 few larger ones. This coiling is generally obscured by the development 

 of matrical material. Total end-to-end contraction is to approximately 

 one-fifth the initial length (Sparrow, et ah, 1941). About midway 

 through this process, it becomes obvious that each chromosome is at 



120 / CHAPTER 5 



