INTRODUCTION. XXV 
operation, at almost any stage, the animal, if disturbed, is 
capable of removing itself to a more quict and secure 
place. 
The process appears to be the result of an internal 
growth of the animal, which becoming too large, the skin 
splits at the margin of the dorsal and sternal arches of 
the three anterior segments of the pereion, the inferior 
arch carrying the legs, inclusive of the coxe. 
The anterior segment of the pereion extends over the 
posterior margin of the cephalon. At this poimt the 
attachment is broken anteriorly, and the lateral disunion 
of the three anterior segments allows their upper surfaces 
to be raised as a movable lid, through the opening of 
which the animal escapes from the old integuments. 
With some exertion, the posterior portion of the body, 
together with the limbs, are withdrawn, after which the 
head and the anterior members are removed, and the 
entire animal is free from the old exuviz, which, resem- 
bling a dead individual, is left, attached to its old position. 
Unless disturbed, the animal, which is now extremely 
soft, generally rests for some time, as if exhausted, near 
the cast-off skeleton. Upon being disturbed, it is capable 
of swimming away immediately. 
Mr. Harry Goodsir, in the Edinburgh Philosophical 
Journal for 1842, has described the process of exuviation, 
as observed by him in the genus Capreila. 
He says that the animal, previously to the commence- 
ment of the process, “lies for a considerable time languid, 
and to all appearance dead. At length a slight quivering 
takes place all over the body, attended in a short time 
with more violent exertions. The skin then bursts behind 
the head in a transverse direction, and also down the 
mesial line of the abdominal surface ; a few more violent 
exertions then free the body of its old covering. After 
