1606 THE STORY OF THE UNIVERSE 



by acquiring the semi-parasitical habit, common to 

 many South American birds, of breeding in the large 

 covered nests of the Dendrocolaptidae, although, ow- 

 ing to increased severity in the struggle for the pos- 

 session of such nests, this habit was defeated. 



The Rhodius anarus, a fish of European rivers, 

 also ensures a quiet retreat for his offspring by a 

 method which is not less indiscreet. At the period of 

 spawning, a male chooses a female companion and 

 with great vigilance keeps off all those who wish to 

 approach her. When the laying becomes imminent, 

 the Rhodius, swimming up and down at the bottom 

 of the stream, at length discovers a Unio. The bi- 

 valve is asleep with his shell ajar, not suspecting the 

 plot which is being formed against him. It is a 

 question of nothing less than of transforming him into 

 furnished lodgings. The female fish bears under- 

 neath her tail a prolongation of the oviduct; she in- 

 troduces it delicately between the mollusk's valves 

 and allows an egg to fall between his branchial folds. 

 In his turn the male approaches, shakes himself over 

 it, and fertilizes it. Then the couple depart in search 

 of another Unio, to whom to confide another repre- 

 sentative of the race. The egg, well sheltered against 

 dangers from without, undergoes development, and 

 one fine day the little fish emerges and frisks away 

 from his peaceful retreat. 



The hermit-crab perhaps knows best how to take 

 advantage of old clothes. He collects shells of Gas- 

 teropods, abandoned flotsam, the first inhabitant of 

 which has died. The hermit-crab (Pagurus Bern- 

 hardus) is a Decapod Crustacean that is to say, he 



