178 HEREDITY AND VARIATION 



parents or, if possible, your grandparents, telling of any mental or 

 physical characteristics they may find repeated in you from an 

 earlier generation. 



Observations. Make notes on as many striking cases of in- 

 heritance as you can. Compare with your own case. 



Conclusion. 1. Are we in any ways like our ancestors? 



2. Are mental as well as physical characteristics inherited? 



3. Do these characteristics seem to be the same as those in 

 your ancestors? 



4. What do we mean by heredity? 



Problem 153 : To study the fine structure of an egg cell. 



Materials. Egg cells, preferably from ascaris (a worm), - 

 stained with iron hsematoxylin to show nucleus and chromosomes ; 

 cells showing fertilization stages; charts; books. 



Observations. Look at the stained cells each lying within a 

 more deeply stained capsule or covering. What structure do you 

 find within it? (Compare figure on page 252, Civic Biology.) 

 Look for the chromosomes within the nucleus. How many can 

 you find? 



NOTE. The chromosomes in the cells of the body are always definite in number 

 for every species of animal and vary from two in ascaris to over 150 in Crustaceans. 

 In man there are sixteen. The chromosomes are believed to carry the hereditary 

 qualities from one generation to the next. 



Examine stained specimens that show, fertilization and study 

 carefully the figure on page 252, Civic Biology. 



NOTE. Before fertilization takes place, the number of chromosomes in each 

 sperm and egg cell is reduced one half. Each cell, so far as the chromosomes are 

 concerned, is now a half cell. 



Conclusion. 1. What happens when fertilization takes place? 

 Study the figure. 



2. If new characters are brought to the new animal or plant 

 by means of the chromosomes, then what part would fertilization 

 play in heredity? In variation? 



Problem 154 : How selection is made. 



Materials. Corn on ear, photographs or description of differ- 

 ent corn plants. 



