JOTTINGS FROM THE BIOLOGICAL LABORATORY 

 OF SYDNEY UNIVERSITY. 



By William A. Haswell, M.A., B.Sc, 

 Lecturer on Zoology and Comparative Anatomy, &c. 



L On A destructive Parasite op the Rock Oyster. 



I was requested some time ago by Dr. Cox, the President of the 

 Fisheries Commission, to examine some samples of oysters from 

 the Hunter River beds, which appeared to be dying in large 

 numbers owing to the attacks of some parasite. On examining 

 the specimens which I received, I found that most of them, when 

 opened, presented on the inner surface of the shell one or more 

 discoloured blisters. In some these raised discoloured patches 

 were of small extent, with a narrow sinuous form, while in many 

 instances a large part of the valve was aifected. In some cases, 

 where the extent of the shell invaded was not large, the oysters did 

 not seem at all affected by it ; in other cases the animal was found 

 to be dead, and in a few cases the shell was completely empty. 



A very slight pressure suffices to break open the blisters, which 

 are covered only by a thin layer of nacreous substance, and their 

 interior is found to be occupied by fine black mud. In the earlier 

 stages, instead of a fair-sized open cavity, there is merely a narrow 

 tunnel bent upon itself, excavated in the substance of the shell, 

 and opening on the exterior at the edge of the valves ; but where 

 the mischief has spread further the greater part of the substance 

 of the shell beneath the blisters has become more or less dis- 

 integrated and readily splits up into soft laminae, with often an 

 infiltration of fine mud between them. In almost every instance 

 I found in the interior of the cavity one or more specimens of the 

 little animal by which the mischief had been elTected,— a very 

 small annelid of the genus Leucodore or Polydora. 



