Il8 . ZOOLOGY. 



carried about to fresh fields, and enjoys a portion of the food 

 broken up by the strong pincers of the crab. Observers claim 

 that the crab offers choice morsels of food to its companion. 

 When the crab by reason of its growth needs a new home it is 

 said to transplant the anemone thereto. These must be looked 

 upon as very remarkable adaptive instincts. Symbiosis is 

 probably more common between animals and plants than 

 among animals. The most interesting of these latter are seen 

 in the so-called " ant-loving " plants, in which the plant pro- 

 duces special homes or special foods for the ants, and the ants 

 in return protect the plant from the ravages of other leaf- 

 cutting ants or hurtful insects. Certain sea-anemones possess 

 unicellular algae imbedded in the cells of the entoderm. These 

 algae derive their nourishment from the wastes of the animal 

 tissues and supply oxygen and possibly other matter to the 

 cells in which they lie. The close relation between the struc- 

 ture and instincts of insects, on the one hand, and the form of 

 flowers, their products and needs, on the other, illustrates a 

 symbiotic adaptation which has long attracted students both 

 of botany and zoology. See Fig. 56. 



157. Library Studies. Make a report concerning the various myrme- 

 cophilous plants. Accumulate all the supposed instances of symbiosis 

 which your library records. How do the lichens illustrate symbiosis ? 



158. The Preying Habit. The effects of this habit are 

 stamped upon the structure and activities of both the pursuer 

 and the pursued. It is in this relation that nature is indeed 

 " red in tooth and claw." While in general the same organs 

 and habits which are of value in the capture of prey are useful 

 in the defense of the possessor, it is possible to find a series 

 of adaptations of an offensive character and others more 

 specially of defensive value. The curved claws and sharp 

 teeth, the stealthy approach, the sudden spring, and the great 

 agility of the one are met by the timidity, the keen senses, 

 the fleetness of the other. We can see that these defensive 

 adaptations must keep pace with the offensive else the prey 

 would be exterminated, which would entail no less surely the 



