212
THE SEAS
.
'
continue 'to swim about and then must either die or nd a
'
crab on which to settle.
In the latter case they attach
themselves by means of tiny books on their feelers to hairs
on the body of the crab, the feelers penetrating the base
of the hair after which the legs of the Sacculina are cast
off and the rest of the body degenerates into a little mass
which passes through the hollow feelers into the crab’s -
body.
It is carried in the blood stream until it reaches the
.
middle of the body where it attaches itself near the stomach,
‘
sending out roots in all directions, while the main mass grows
"
larger and larger until it gets pressed against the inside
of the shell about the middle of the under side of the body.
.
The next time the crab moults the parasite pùshes its way
-
'
out bef0re the new shell has had time to harden and there '
,.
assumes its nal tumour—like shape.
'
The parasite usually lives some three or four years
and from the time it escapes to the exterior the host
cfab never mou1ts, all its reserve of food and strength gO
to supply the needs of the parasite.
It is only when the
Sacculina dies that the crab is able to resume growth and
.
moult at the usual
It is a very interesting faCt
that male crabs which are infected in this way gradually
assume the appearanCe of females, developing a broad
instead of a thin abdomeu, smaller claws, and certain
small legs on the hinder end of the body which are normally
only possessed by the females.
About seventy per cent. of
infected male crabs show various stages in this process
but
‘
_
.
infected femaleS on the other hand show no signs of becoming
'
like males.
An elaborate theory of the causation of sex
'
'
has been based on this sex change in parasitiz_ed crabs.
-
…
of this are out of place here, but the gist of it is
-
'that the presence of the parasite causes the active male
‘
to lead the more sedentary life of the female, and to eat
more in
.
order to counteract the abnormal drain on its
"
THE SEAS
.
'
continue 'to swim about and then must either die or nd a
'
crab on which to settle.
In the latter case they attach
themselves by means of tiny books on their feelers to hairs
on the body of the crab, the feelers penetrating the base
of the hair after which the legs of the Sacculina are cast
off and the rest of the body degenerates into a little mass
which passes through the hollow feelers into the crab’s -
body.
It is carried in the blood stream until it reaches the
.
middle of the body where it attaches itself near the stomach,
‘
sending out roots in all directions, while the main mass grows
"
larger and larger until it gets pressed against the inside
of the shell about the middle of the under side of the body.
.
The next time the crab moults the parasite pùshes its way
-
'
out bef0re the new shell has had time to harden and there '
,.
assumes its nal tumour—like shape.
'
The parasite usually lives some three or four years
and from the time it escapes to the exterior the host
cfab never mou1ts, all its reserve of food and strength gO
to supply the needs of the parasite.
It is only when the
Sacculina dies that the crab is able to resume growth and
.
moult at the usual
It is a very interesting faCt
that male crabs which are infected in this way gradually
assume the appearanCe of females, developing a broad
instead of a thin abdomeu, smaller claws, and certain
small legs on the hinder end of the body which are normally
only possessed by the females.
About seventy per cent. of
infected male crabs show various stages in this process
but
‘
_
.
infected femaleS on the other hand show no signs of becoming
'
like males.
An elaborate theory of the causation of sex
'
'
has been based on this sex change in parasitiz_ed crabs.
-
…
of this are out of place here, but the gist of it is
-
'that the presence of the parasite causes the active male
‘
to lead the more sedentary life of the female, and to eat
more in
.
order to counteract the abnormal drain on its
"