300 Prof. :\I'Tnto.sli's Notes from the 



about fourteen havinc: been examined. He found that P<>h/- 

 dora chiefly affected those oysters on tlie surface of or buried 

 iu the nuid, a feature probably not unconnect.'d with the fact 

 that tubes of mud are fashioned by the annelid at its apertures 

 iu the shell. The idea that removal of the shells from mud 

 would lessen the liability to attack may have some basis, 

 since, as mentioned, mud is necessary for the manufacture of 

 the tubes which project beyond the apertures in the shell ; 

 but the annelid also makes these tubes of the dcl)ris from its 

 borings in aluminous shale. It must not be supposed, how- 

 ever, that the jjlacing of the oysters on a bed of shells will 

 have the effect of freeing them from the annelids, the business 

 of which is to bore into all shells and similar solid bodies. 

 His diagnosis of oysters "badly infested with worms" as 

 having a thick rounded outline and devoid of thin sharp 

 edges will not suit British oysters, such as those from Whit- 

 stable, many of which have thin edges, though the shell is 

 honeycombed by the worms. Moreover, in the British oysters 

 the apertures of the tubes occur all over the shell, and the 

 same occurs in certain examples from Australia. He is of 

 opinion that the oysters were infected before removal from 

 the mangrove-flats to the beds, but, as the swarms of pelagic 

 larvce carry the species everywhere, this is not of much con- 

 sequence. The view that on the natural beds (on the 

 raangrove-flats) the oysters appear to overcome the worm — 

 that is, the postlarval form — by quickly enclosing it with a 

 thick layer of shelly matter before it has had time to establish 

 itself is more than doubtful. The young annelid may settle 

 on the shell quite out of the reach of any such secretion, just 

 as it does on the limestone, chalk, and shale. The postlarval 

 worm is not different in this respect from the postlarval 

 Cliona, the boring sponge, which likewise settles on the 

 oyster irrespective of any shelly secretion, and is even more 

 destructive than Fohjdora. Besides, an examination of the 

 massive pearl-shells from Thursday Island, for which this 

 University Muf^eum is indebted to Mr. James R. Tosh, will 

 show that the postlarval boring mollusks, like the boring 

 sponges, follow similar habits and settle in numbers on the 

 valves irrespective and out of reach of any shelly secretion. 

 Folydora is capable of perforating harder shells than those 

 of the oyster, and its ravages are perhaps best seen in massive 

 shells such as those of Chuvia. 



The keyhole outline of the tubes " furthest from the edge 

 of the oyster " is probably due to the coalescence of the tubes 

 lo foim a loop, for the tunnels of Polydora, so far as observed, 

 are circular, and thus in marked contrast to the tunnels of 



