50 LABORATORY DIRECTIONS 



1. RESTING STAGE. Chromatin scattered throughout the 

 nucleus in the form of small granules. 



2. PROPHASE. Chromatin becoming arranged in masses, 

 usually forming a coiled thread, the spiremc. 



3. METAPHASE. The chromatin thread has broken into 

 chromosomes which have become arranged in the equatorial plate. 

 In this stage each chomosome has split longitudinally but be- 

 cause of their minute size in Cerebratulus the individual chomo- 

 somes are not readily observable. 



4. ANAPHASE. Chromosomes moving toward each pole of 

 the spindle. 



5. TELOPHASE. The construction of the two daughter 

 nuclei. This is usually accompanied by a cleavage of the cell, 

 whereby the two daughter nuclei become the nuclei of two daugh- 

 ter cells. 



REFERENCE 



Wilson, E. B., 1900. The Cell in Development and Inheritance. 

 MacMillan. 



EMBRYOLOGY OF CEREBRATULUS 



Classification : Phylum Plathelminthes, Class Nemertini, 

 Order Heteronemertini. 



Cerebratulus is a marine worm which lives in burrows on 

 sandy beaches. Its reproduction is by the sexual method. When 

 the females reach maturity they discharge enormous numbers of 

 eggs into the s'urrounding water. At the same time the males 

 discharge myriads of small, motile spermatozoa into the water. 

 These spermatozoa, through their powers of locomotion, come 

 into contact with the eggs liberated by the females. Under nor- 



