INTRODUCTION. xxv 



operation, at almost any stage, the animal, if disturbed, is 

 capable of removing itself to a more quiet 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 coxae. 



The anterior segment of the pereion extends over the 

 posterior margin of the cephalon. At this point 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 together with the limbs, are withdrawn, after which the 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 exuviae, 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 PhilosojjJiical 

 Journal for 1812, has described the process of exuviation, 

 as observed by him in the genus Cajjrella. 



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 



