43 



time the worm has been in the shell. The grooves are deepest 

 near 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 l)y 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 supposed, 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 l»ody, or mechanically 

 by means of its bristles. My opinion is that the worm does not 

 here into the substance of the shell at all in the strict sense of the 

 word. 



How the Worms effect an entrance into th.e 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 appearances pre- 

 sented may be accounted for without supposing that the worm 

 deliljerately 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 were those of the Poly dor a ciliata. They 

 were found on the sides of the membranous tubes of the worm, 

 in little transparent sacs, each cluster somewhat less in diameter 

 than the body of the worm, and each sac containing between 50 

 and 60 eggs. I placed some of these egg-sacs in a test tube and 

 kept them for six days, during which time most of the eggs 

 hatched out. On examining a cluster under the microscope, I 

 observed the newly hatched larvse swimming about in the egg-bag, 

 and by means of a dissecting needle, I ruptured the wall and 

 allowed them to escape. They swim very rapidly by means of 

 the oral and anal wreaths of cilipe and the tufts of long stiff setfe, 

 which they only used occasionally. They appear to jump or 

 skip when the bristles are brought into play, and are conse- 

 quently very difficult to follow under the microscope. At birth the 

 body is about twice as long as broad, and consists of six segments. 

 The antennae are represented by small rounded lobes, the eyes are 

 four in number, two near the mesial line, and two a little further 

 forward and widely separated. On each side of the body there are 



