20 



THE ANIMAL CELL 



[CH. II. 



cells; such as in the number of chromosomes, and the relative 

 importance of the different stages. All attempted here has been 

 to give an account of a typical case. The phases may be summarised 

 in a tabular way as follows (from " Quain's Anatomy ") : 



1. Resting condition of mother nucleus 



(fig. 19). 

 (2. Close skein of fine convoluted filaments 



(% 20). 



j 3. Open skein of thicker filaments. Spindle 

 V. appears (fig. 21 A). 



4. Movement of V-shaped chromosomes 



to middle of nucleus, and each splits 

 into two sister threads (fig. 21 B). 



5. Stellate arrangement of V filaments at 



equator of spindle (fig. 22). 



6. Separation of cleft filaments and move- 



ment along fibres of spindle (fig. 24 A 

 and B). 



7. Conveyance of V filaments towards poles 



of spindle (fig. 24 c). 

 , 8. Open skein in daughter nuclei. 

 { 9. Close skein in daughter nuclei (fig. 25). 

 . 10. Resting condition of daughter nuclei 

 (fig. 25). 



NETWOBK OR RETICULUM . 



SKEIN OR SPIREM 

 CLEAVAGE . 



STAR OR MONASTER . 

 DIVERGENCE OR METAKINESIS 



DOUBLE STAR OR Di ASTER 



DOUBLE SKEIN OR DISPIREM 

 NETWORK OR RETICULUM . 



The Ovum. 



The ovary is an organ which produces ova. 



An ovum is a simple animal cell ; its parts are soen in the next 

 diagram. 



It is enclosed in a membrane called the zona pellucida or vitelline 

 membrane. The body of the cell is composed of protoplasm loaded 



Nucleus or germinal vesicle. 



Nucleolus or germinal spot. 



.Space left by retraction of 

 protoplasm. 



Protoplasm containing yolk 



spherules. 



../. Vitelline membrane. 



FIG. 26. Representation of a human ovum. (Cadiat.) 



with granules of food material, called the yolk or vitellus. The 

 nucleus and nucleolus are sometimes still called by their old names, 

 germinal vesicle and germinal spot respectively. The attraction sphere 

 is not shown in the diagram. 



The formation of ova will form the subject of a chapter later on, 



