PERSONAL AND CIVIC HYGIENE 



345 



sperm cell, is much reduced in size so as to be correspondingly very active 

 and motile ; while the other, called the egg, has the food yolk stored up 

 in it, with a consequent increased size, which prevents more than very 

 slight independent movement, if any. 



3. Can you distinguish between sexes among Paramoecia ? Lilies ? 



Note. Along with differences between the sexes for purposes of 

 division of labor, such as noted above, we note other secondary differ- 

 ences between them creeping in, so that we may readily recognize male 

 and female individuals. We readily distinguish a male bird from a hen. 

 Note the differences between a peacock and a peahen. Give other ex- 

 amples among higher animals. 



3. VARIOUS MEANS USED BY SPERM CELLS IN REACHING 

 EGGS (OPTIONAL) 



Observation. Fill in the following tabulation, wherever possible : 



d. Heredity 



" Nature loves variety, so that the best will survive. She has never 

 yet made two eggs or two sperm cells exactly alike." JORDAN. 



