DIFFERENTIATION OF INDIVIDUALS AND ADAPTATION 



123 



be so described. The aphides, although captives, are nour- 

 ished, often at great expense of labor to the ant, on the food 

 which they most prefer, and in return the ants use the sweet 

 secretions of their bodies as food. Certain hermit-crabs, 

 whose habit it is to occupy gasteropod shells as a home into 

 which they insert the soft posterior part of the body, cultivate 

 friendly relations with a sea-anemone which becomes attached 

 to the shell, often with the active help of the crab. The 

 anemone is supposed by some to conceal the hermit and to help 



FIG. 57. 



FIG. 57. Hermit-crab in the shell of a Gasteropod. After Morse. 



Questions on the figure.^-What structural adaptations has the hermit-crab 

 to this mode of life? What conceivable gain has such a habit? What animals 

 are cited as symbiotic with the hermit-crab ? 



protect it by means of its nettling cells, and in return is carried 

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

 up by the strong pincers of the crab. Observers have claimed 

 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- 



