IV] LIFE-HISTORY AND ENVIRONMENT 51 



then attack the muscle. If this happens, the empty 

 shells of the oyster alone are left, perhaps uninjured 

 and with nothing to indicate the mode of death. 



Certain sponges (Cltone) bore into the thickness 

 of the shell valves just as they do in the scallops of 

 our seas. The valves are honeycombed in all 

 directions until they become completely rotten. 

 More serious, however, than these animals are the 

 starfish. Herdman records the destruction of be- 

 tween 200 and 300 a day when the s.s. Violet, in 

 the fishery of 1905, was dredging for pearl oysters. 

 This must give a huge total for the starfish living 

 on the paars. 



Starfishes have, too, such powers of regeneration 

 that, other conditions being favourable, they are 

 little disturbed by being torn into two. They are 

 very voracious, and have reduced the opening of 

 oysters to a fine art ! In one case Herdman and 

 Hornell considered that the disappearance of 5| mil- 

 lion oysters in a year was probably due to this enemy. 



So much for the environment. It must not be 

 forgotten, hoAvever, that to any one oyster the other 

 brother oysters are also parts of the environment. 

 If therefore the young oysters are overcrowded, a 

 large number will die through interference with 

 nutrition. The competition for food is a greater 

 factor in the history of this universe than perhaps 

 many of its inhabitants believe ! 



4—2 



