INTRODUCTION 



body. The two spheres separate from each other and send out radiat- 

 ing filaments, forming a double star, called the amphiaster. They are 

 connected together, however, by filaments in the form of a spindle 



Fig. 3. Diagram showing the prophases of karyokinesis (Wilson). 



A, resting-cell : c, attraction-sphere containing two centrosomes. B, early prophase, the nucleus 

 containing a continuous spirem, the nucleolus still present : a, amphiaster. C, disappearance of the 

 primary spindle and passage of the centrosomes to opposite poles of the nucleus (the nucleolus has 

 disappeared) . D, another type of prophase, in which the primary spindle persists. , later prophase, 

 in which a new spindle is formed within the nucleus. F, completion of the karyokinetic figure : 

 ep, equatorial plane of chromosomes. 



(the central spindle), which lies next the nucleus, gradually encroach- 

 ing upon it. The substance of the amphiaster and the spindle is called 

 archoplasm. As the spindle is formed, the membrane of the nucleus 



