110 THE WORM DISEASE IN OYSTERS. 



Symptoms 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. More- 

 over, by looking along the anterior margins of the valves, the entrances to 

 the worm tubes will, on close inspection, be readily seen ; those openings 

 furthest removed from the edges of the shell having a Jcet/hole-Uke out- 

 line, whist 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 posterior margins, but rarely on other 

 parts. On opening the diseased oyster, the valves will be seen to possess a 

 series of blister-like structures, which are very variable in shape and extent, 

 .usually they are 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 be seen a quantity of light brown mud in which 

 the worms are embedded. Each worm has its own collection of mud, and 

 from it a membranous tube often extends a short distance 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 enclosed by the thin layer of shell deposited 

 by the oyster. "When viewed in section the opening of the tube is semi- 

 circulai", the older part of the shell forming the base, and the newer layer 

 the half-circle ; or there are two openings, each consisting of three-fourths 

 of a circle, with a space connecting them together, and bounded above and 

 below by linear layers 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, 

 varying according to the length of time the worm has been in the shell. 

 The grooves are deepest pear the edges, and gradually get shallower inwards. 

 During my observations I found about twenty examples in which very young 

 worms had just entered the shells, and in all these cases the worms were 

 surrounded by large patches of mud, and a thin membranous covering 

 deposited by the oyster. On the removal of this mud, the surface of the 

 old shell was quite smooth, without any trace of a groove — a lens when 

 applied to the spot failing to show any erosion. The only means by which 

 the place occupied by the worm could be detected was by the presence of 

 the edges of the thin membrane formed by the oyster. The above-mentioned 

 facts have an important bearing on the question as to how the worm gets 

 into the shell, which is a much simpler process than has hitherto been sup- 

 posed, inasmuch that it does not entail any far-fetched theories about the 

 worm boring into the shell, with the assistance of an acid secretion from the 

 body, or mechanically by means of its bristles. My opinion is that the worm 

 does not bore into the substance of the shell at all, in the strict sense of 

 the word. 



Sow tJie Worms effect an entrance into the Oysters. 



Before entering into details it will be necessary to take into consideration 

 the habits of the young worm, which will, when fully stated, show that the 

 boring theory is out of the question ; and, further, that sections of the shell, 

 if carefully examined, furnish sufficient evidence to show that all the appear- 

 ances presented may be accounted for without supposing that the worm 

 deliberately drills an opening into the solid shell. On the third day after 

 my arrival at Newcastle, I found several clusters of ova, which I concluded 



