43 REPORT — 1855. 



their integumentary tissues periodically*. This remark holds equally true as 

 regards the lining membrane of the alimentary canal, which is cast in con- 

 nexion with the external skeleton. There is no appreciable difference in the 

 habits of the animal more immediately before the casting of the skin than at 

 any other period. It appears to swim about just the same until the hour of 

 moulting arrives, when it seeks a place of comparative security where it may 

 remain the desired length of time that may be necessary without fear of 

 interruption. 



The opportunities that have been most favourable for our observations 

 have been when the animals, confined in glass jars, have occasionally chosen 

 a position against the upright walls. 



They grasp with their anterior foot or feet some fixed ground, weed, or 

 secure material as an anchorage, resting the entire side against the glass. 

 Here the little creature commences its labour, which appears to be one of 

 no great discomfort, if we may judge from the small amount of disquietude 

 with which the operation is conducted. Almost at any stage the animal has 

 the capability of removing, if it be disturbed, to another spot out of reach. 



The process appears to be the result of an internal growth of the animal, 

 which becoming too large for the skin, it splits. This is produced at the 

 maro-in whore the dorsal and sternal arches of the three anterior segments of 

 the pereion (thorax) meet, the inferior arch carrying the legs, inclusive of 

 the coxEe (epimerals) attached to them ; a fact, which identifies, we think, the 

 relation of the (so-called) epimerals with the sternal rather than the dorsal 

 arch. 



The first of the two gnathic segments of the pereion which overrides 

 anteriorly the cephalic ring is broken at that point from its attachment with 

 it, and in conjunction with the two next succeeding segments it becomes a 

 moveable lid, as it were, to the case in which the animal resides. 



After some tolerable exertion, the posterior portion of the animal, together 

 with its limbs, is withdrawn from its normal position, and ultimately becomes 

 entirely liberated from the skin, to which the animal now remains attached 

 by the head and the anterior members only. A few more struggles, and the 

 creature is free of the whole of the dead exuviae, which 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 ; should, 

 however, there be any cause, it is perfectly capable of swimming away 

 immediately. 



In Caprella, Mr. Henry Goodsir (Edinburgh Philosophical Journal, 1842) 

 remarked that the animal, before the process commenced, " 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 this 

 the animal remains for a considerable time in a languid state, and is quite 

 transparent and colourless." 



The new creature is a perfect representation of the old one slightly 

 enlarged, and, according to our own observations, every hair is produced 

 complete ; though Prof. Edwards believes that this is not the case, but that 



* Mr. Bell, in his Introduction to the ' History of the British Crustacea,' has, upon the 

 authority of Mr. Couch, stated (iu a note, page Ixi), " that the families in which the eyes 



are always sessile in their adult growth do not exuviate or voluntarily throw oflF 



their limbs." 



