34 HEREDITY 
Other examples show by means of a series of mollusks the 
range of color variation within a single species of West Indian 
Sun Shell, variation of sculpture within a single genus of land snail, 
and variations about the normal type of the common scallop. 
The struggle for existence is portrayed by the meadow mouse, 
surrounded by its many enemies and yet continuing 
Struggle for 
Rete to mainta n an existence by virtue of its great birth rate. 
The simpler features of the laws of Heredity as eluci- 
dated by Mendel and his followers are illustrated by the inheritance 
of seed-coat color in the common pea, the color of sweet 
peas, and the coat-color of rats. 
[Return to the elevators and ascend to the second floor.| 
Heredity 

ENLARGED MODEL OF A RADIOLARIAN 
