268 THE GREAT BARRIER REEF. 



to old shells in deep water, which it honeycombs in every direction. This parasite is soon got rid 

 of, by the exposure of the affected oysters to light and sunshine on the banks. 



Several species of birds, including notably the so-called oyster-catcher, Hcematopus longirostris, 

 and the numerous members of the crane tribe that frequent the oyster-banks at ebb-tide, prey to 

 some extent on the young oyster brood. Next to the borer, however, the greatest amount of 

 injury to the oyster-cultivator's growing crops is probabiy committed by the innumerable species 

 of crabs that infest the beds and banks. 



A destructive agency that has caused great losses to the oyster-growers of New South Wales, 

 and of which there was some suspicion of its having made its appearance among the oysters in 

 Wide Bay, is what has been styled the "Worm Disease." This disease is characterised by the 

 presence, within the oyster-shells, of patches of mud, which are more or less completely covered in 

 by a shelly or membranous re-deposit. One or more small worms, Leucodore ciliata, are almost 

 invariably found enclosed within these mud cavities, and from these, through a tubular channel, 

 they maintain a communication with the outside water. This worm is usually credited with the 

 primary origin of the so-called disease ; but on the strength of a slight passing acquaintance made 

 with it in New South Wales, and of the facts relating to it that have been published, the author 

 is inclined to believe that the organism is only an accompaniment, and not the cause, of the disease. 

 Mr. Whitelegge, of the Sydney Museum, who has approached the subject from the standpoint 

 of the worms being the originators of the disease, has offered the following remarks, after making 

 investigations concerning its occurrence at the Hawkesbury River: — "The principal home of the 

 worm appears to be on the mud-flats about low water-mark. The oysters from this region, the 

 Hawkesbury, were invariably infected with the worm, particularly those which lay loose on the 

 surface or were partially buried in the mud. Those oysters which were fixed to some solid sub- 

 stance, and elevated ever so little above the mud, were comparatively free from the pest." The 

 foregoing testimony goes far to show that this so-called worm disease is essentially a " dirt 

 disease." It is only in a muddy environment, unsuitable for the healthy growth of the oyster, that 

 it spreads; and that it is the mud, and not the oyst&v per se, that attracts the worm, is demonstrated 

 by the fact that oysters elevated but a few inches above the muddy stratum are relatively 

 free from the affection. 



The inference arrived at by the author concerning the occurrence and manifestations of this 

 disease, is that the oyster, through the foulness of its surroundings, draws into its shell cavity, 

 by the ciliary action of its gill.s, a greater amount of mud than it can get rid of, and that the 

 worm, in its free-swimming embryonic state, being drawn within this cavity by the same ciliary 

 current, settles down with alacrity within so congenial a mud-lined cradle. The worm, 

 Leucodore ciliata, under discussion, enjoys an almost cosmopolitan distribution. Its habitat, as 

 recorded in Dr. Johnson's catalogue of non-parasitic worms, in the year 1S65, is as follows: — 

 " Found living between seams of slaty rock near low-water mark, and burrowing in the hne soft 



