II. MUTUAL 

 ADJUSTMENT 



ARIOUS phenomena of 

 association between non- 

 competing species are 

 manifest alike in terres- 

 trial and aquatic socie- 

 ties. The occurrence of 

 producers and consumers 

 is universal. Carnivores 

 eat herbivores, and para- 

 sites and scavengers fol- 

 low both in every natural 

 society. Symbiosis is as 

 well illustrated in green hydra and green ciliates as in 

 the lichens. The mutually beneficial association be- 

 tween fungus and the roots of green plants is as well 

 seen in the bog as in the forest. The larger organisms 

 everywhere give shelter to the smaller, and many ex- 

 amples, such as that of the alga, Nostoc, that dwells in 

 the thallus of Azolla, or the rotifer Notommata parasita 

 that lives in the hollow internal cavity of Volvox, occur 

 in the water world. 



We shall content ourselves here with a very brief 

 account of two associations, one of which has to do 

 mainly with a mode of getting a living, the other with 

 providing for posterity. The first will be insectivorous 

 plants; the second the relations between fishes and 

 fresh-water mussels. 



282 



