Ontlij Mart lie La/ioralori/j S'f. Andrews. 303 



and have no relation to " blisters," iind the position is further 

 shown by the borino^ of the annelid in chalk, limestone, 

 aluminous shale, and sandstone, where tliere is no possibility 

 of the secretion of a "thin membranous" layer to keep the 

 intruder out. As shown by Dr, Carazzi, the conditions indi- 

 cated by "Slv. AVhitelegge pertain tor the most part to the 

 action ot Polyduta Ivplura. 



The notion that boring does not occur because no "grooves " 

 were visible may be equally applied to the baring sponges, 

 Sipunculi, Plioronides^ and other forms. Besides, no grooves 

 are necessary wliereachink between the shelly layers permits 

 the annelid to form its tunnels of mud, as indicdted in the 

 foregoing paragraph. 



The tendency to secrete a nacreous coating to shut off 

 sources of irritation is observed in many moUusks, and is 

 taken advantage of, for instance, by the Cliinese in the coating 

 of their josses with the nacreous layer and in the artitiiiil 

 formation of pearls. Blister after blister may thus be formed 

 by different perforations. It is interesting that the boring 

 sponges do not cause the same iiritation as the excreted mud 

 of Folydora, their minute perforations on the inner wall of 

 the shell being rapidly coated by the shelly secretion; but 

 their great number and persistent character have ultimately 

 a serious effect on the health of the oyster. The decomi»o- 

 sition of this excreted mud of Fulijdora is certainly a source 

 of danger to the uiollusk. 



'J hat the annelids do not thrive unless in living oysters 

 which cause currents, and thus bring the commensals food, is 

 negatived by the fact that vast numbers bore in limestone 

 rocks and shale, where no living mollusks and no favourable 

 currents are. They have, indeed, been kept alive in shale 

 for months 50 miles from the sea. All that can be said on 

 this head is that they are very abundant on living oysters. 



It is quite possible that the boring is best carried out when 

 the annelid settles after the pelagic stage. The " helplessness " 

 of the adult when removed from its tube is no proof that it 

 is incapable of boring. Any other adult borer, for example 

 Jfodecaceria or SabelUi suxicava, would, when removed from 

 its tube, be equally helpless. 



The statement that in certain instances the annelid " lives 

 completely within the shell, and the ends of the tube have 

 no connexion with the outer world except when the oyster 

 is open," is exceptional. As far as observed, a like condi- 

 tion has not been seen in this country nor in one hundred 

 and twenty oysters from fittecn Australian be<ls, iucludino- 

 those from Hunter River (Newcastle) kindly j)resented to 



21* 



