Ml'lOS/S Jf) 



cavity itself. The cytoplasm of the cnj^ appears vacuolated, 

 that is, appears to contain empty spaces. Dark-staining bodies, 

 the chromosomes, will be seen in the nucleus. Search the cells 

 for typical examples of the stages in n»itotic cell division as 

 called for below. 



It may not prove an easy task to find just the stage desired, 

 but only as a last resort should assistance be recjuested ()f the 

 instructor. The difficulty lies in the fact that the sections are 

 very thin anil therefore a complete picture of what is desired may 

 not be found in a given section unless it passes through the proper 

 plane of the cell. Avoid the study and drawing of such partial 

 figures and represent egg cells at least an inch and a half in 

 diameter. 



In the following paragraphs the stages or phases of mitosis 

 are arranged in the order in which they occur. Although phases 

 are referred to for descriptive purposes it is to be kept in mind 

 that mitosis is a continuous process and that the stages here 

 described overlap in varying degrees. The term phase or sfngr 

 is employed as a name for the completion of certain events regard- 

 less of whether these events are completed before or after another 

 begins. 



Early Prophase Stage. — As cell tli vision begins, the chromatin 

 substance of the nucleus appears to form a long, coiled thread. 

 Consider that in sections only pieces of such a coiled thread could 

 appear and then note in the demonstration of this stage the 

 deeply stained, elongate pieces of chromatin to be seen in the 

 nucleus. 



Late Prophase. — The thread is resolved into a number of 

 distinct slender bodies, each of which is called a chromosonw. 

 In Ascaris there are four of these. The small number of chromo- 

 somes is one of the advantages of Ascaris material for this stutly 

 rather than cells from the frog where 24 chromosomes appear. 

 In well-prepared material there will be ob.served in the cytoplasm 

 close to the nucleus two dense areas of granules called the a.s7<;-.<?. 

 Ivich aster contains a dark center, the centrosome, a.ssociated with 

 radiating fibrils, the astral rays, reaching out into the surround- 

 ing cytoplasm. Between the centrosomes, which come to be 

 located at opposite poles of the cell, there extend similar delicate 

 fibrils which collectively are called the spindle. The spindle 

 together with two asters constitutes what is known as the 

 achromatic figure, or amphiaster. Sometime during the processes 



