INTRODUCTION. 
75 
Bpcurity, and seldom leave it even though disturbed. 
Although weak and languid, they are continually 
giving various movements to the body, but without- 
shifting their station. The back is sometimes bent 
outwards, and soon after resumes its natural position, 
and the head is elevated, and speedily drawn down 
again. At other times, the anterior part of the body 
makes two or three very rapid vibrations to the right 
or left ; while less perceptible motions are communi- 
cated to the different rings, some of which are consi- 
derably dilated, and others contracted. The effect of 
these alternate swellings and contractions soon be- 
comes apparent, for the outer skin, now rendered dry 
and rigid, by the subtraction of the juices by which it 
was previously nourished, begins to split on the back 
of the second or third segment, and discloses a por- 
tion of the new integument. The rent being once 
commenced, is easily extended by the dilatation of 
the body, from the first to the fourth segment, and 
thus leaves a considerable part of the back unco- 
vered. This part of the body is no sooner free 
than it is curved upwards, a movement by which the 
head is disengaged from its old envelope, and raised 
through the fissure. The head is then reclined on 
the case that formerly contained it, and nothing re- 
mains but to withdraw the hinder part of the body, 
which is done by contracting the segments, and 
drawing them towards the head till they reach the 
opening. 
All these operations, apparently so laborious, are 
