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 by the oyster. The above mentioned 
facts have an important bearing on the question as to how the 
wa rn gets into the shell, which is a much simpler process than 
ha 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 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. 
IIow the 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 appearances pre- 
sented 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 J concluded were those of the Poly dor a ciliata. They 
were found on the sides of the membranous tubes of the worm, 
in ] ’ ';tlc 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 larvae 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 cilise and the tufts of long stiff setae, 
v hich they only used occasionally. They appear to jump or 
skip when the bristles arc 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 
