THE DIVISION OF THE PROTOPLAST 



(17 



The achromatic figure develops in typical cases as follows (Fig. 48). 

 Lying in the cj'toplasm neai* the nucleus is a centriole. As the prophasic 

 alterations within the nucleus begin, the centriole divides if not alroad.x- 

 double, and the daughter centrioles move slowly apart. About each 



Fig. 47. — iSection of spennary of crayfish {Potamobius), .showing numerous stages of mitosi.-s. 

 {Courtesy of General Biological Supply House, Inc., Chicago.) 



of them there appears in the cytoplasm a system of radiations known as 

 an aster. Between the two may be seen a bundle of lines called the 

 central spindle, all three parts together constituting an amphiaster. The 

 centrosomes continue to diverge, the asters increasing in prominence, 

 until they reach opposite sides of the nucleus. By the time they reach 

 these positions, and often before this, the nuclear materials complete 



