42 



tained of the habits of the worm, it appears that a large amount 

 of mud is necessary to its existence, and that the more muddy 

 the place, the better the worm thrives ; such being the case, it is 

 reasonable to suppose that those oysters which are lixed on some 

 solid body, and somewhat above the surface of the mud, will 

 liave a better chance of escaping the ravages of the worm, than 

 those which are partially buried in mud or lying loose on the 

 surface. I conclude, therefore, that if some loose material, such 

 as stones, old shells, &q , was placed on the mud-flats for the spat 

 to set upon, removing it from direct contact with the mud, that 

 the prevalence of the worm would be considerably diminished. 

 In the absence of such material, the worms have no other alter- 

 native but to fix on the oysters as a place of refuge. 



Sjpaptoms of the Disease. 



Oysters which are badly infested with worms may be detected at 

 a glance by their thick rounded outline, and the absence of thin 

 sharp edges. Moreover, by looking along the anterior margins of 

 the valves, the entrances to the worm tubes will, on close in- 

 spection, be readily seen ; those openings furthest removed from 

 the edges of the shell having a keyhole-like otitline, whilst those 

 on the actual margins are semicircular. In the majority of cases 

 the worms are found on the anterior margins of both the upper 

 and lower valves, and frequently on the postei'ior margins, but 

 rarely on other parts. On opening the diseased oyster, tlie valves 

 will be seen to possess a series of blister-like structures, which are 

 very variable in shape and extent, usually they ai'e more evident 

 on the lower valve than on the upper. On pressing the surface 

 of these blisters with the point of a knife, it readily yields, and 

 underneath will l)e seen a quantity of liglit brown mud in which 

 the worms are embedded. Each worm lias its own collection of 

 mud, and from it a membranous tube often extends a sliort dis- 

 tance beyond the edge of the shell. The tube is invariably 

 curved, but it is usually curved in such a way that the entrance 

 and the outlet are in close proximity to each other, the inlet and 

 outlet being often inclosed by the thin layer of shell deposited l)y 

 the oyster. When viewed in section the opening of the tulje is 

 semicircular, the older part of the shell forming the base, and the 

 newer layer the half-circle ; or thei'e are two openings, each con- 

 sisting of three-fourths of a circle, with a space connecting them 

 together, and ])ounded above and below by linear layei-s of shell. 

 On removing the thin shelly matter it will be seen that the inner 

 surface retains all the inequalities of the mud over which it was 

 deposited, and forms a sort of mould of the inclosed mud, and 

 rarely exhibits any distinct groove except near the edge. The 

 older parts of the valves upon which the worm rests, exhibit 

 grooves of certain depths, ^'arying accorxling to the length of 



