358 



GENERAL PRINCIPLES 



743. The polymorphism found in many flowers, as a device 

 for securing cross fertilization, has already been described. A 



FIG. 224. Passage ways of the "white-ants" in a post. The termites avoid 

 the light, ordinarily, and hence construct tunnels of mud to cover their runways. 

 These tunnels are often very extensive and much labor is involved in their con- 

 struction. This is performed by the numerous small workers. Xi/2. 



very peculiar type of polymorphism occurs among spiders and 

 butterflies. A number of species of spider are known to pro- 



