INTRODUCTION 



27 



chr- . 



-J3, 



-cifir 



Fig. I.— Diagram of Nvclear DmsioN. 



A. — Cell with nucleus — «,and centrosomes 

 — c.f, preparatory to division. The chromatin 

 has become thickened so as to form a spiral 

 thread — chy. 



B. — The nuclear membrane has disappeared. 

 -Jd/ Delicate threads radiate from the centrosomes, 



and form the ' nuclear spindle,' in the equator 

 of which eight chromosomes or nuclear loops 

 {chr) are arranged: these have been formed by 

 the spiral thread of chromatin in A becoming 

 broken up. 



C. — The chromosomes have each become 

 split longitudinally into two, and are about to 

 be drawn apart by means of the spindle-threads. 

 (For the sake of clearness only four of the 

 eight chromosomes are indicated.) 



D. — The daughter-loops pass towards the 

 poles of the spindle. 



E. — The body of the cell has undergone 

 division: each of the resultant cells contains a 

 centrosome and eight nuclear loops. 



