124 



ZOOLOGY 



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- 



FIG. 58. 



FiG. 58. Argynnis cybele on thistle. Natural size. Photo by Folsom. 



Questions on the figure. For what purpose does the butter fly visit the 

 thistle? What special adaptations does the butter fly possess for this mode of life? 

 What is the gain to the thistle from the visits ? 



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. 58. 



161. Library Studies. Make a report concerning the various myrmecophilous 

 plants. Accumulate all the supposed instances of symbiosis which your library 

 records. Lichens, among plants, are considered to illustrate symbiosis. How? 



