ON OUR PRESENT KNOWLEDGE OV THE CRUSTACEA. 51 



As to the lower forma, such as the Edriophthalma, it was long assumed, on 

 the authority of Professor Bell, who relied on the assertion of the late Mr. J. 

 Couch, that the animals of this order never shed their skin at all, but con- 

 tinue adding to and increasing it until they arrive at tho adult stage. Those 

 who have observed these animals, and seen how the old skin, in a not very 

 long period of time, is liable to become iucrusted and overgrown with foreign 

 material, must rejoice to know that, like their higher neighbours, these animals 

 can at certain periods of their existence eject their old skin, and swim about 

 in a new one, fresh and clean. 



This fact may easily bo demonstrated by any who may like to retain a few 

 specimens in a glass tank, when the exuvia) will be seen soon to strew tho 

 bottom as dead animals, but which, on close examination, will be found to be 

 the remains of the cast-off skins. 



I have kept these creatures long in small vessels, and watched them closely 

 for years, and have seen them shed their exuviaj not unfrequently. 



Tho manner of so doing appears to be upon the same plan as that of tho 

 higher forms, such variation as takes place being consistent only with tho 

 variated conditions and forms of the animals. The animal, having no cara- 

 pace, escapes from the old skin by a separation immediately behind the 

 cephalon, between it and the pereion ; the pereion splits along the lateral 

 walls just above the coxal plates of the legs. This separation corresponds 

 with the lateral opening between the carapace and the legs in the higher 

 orders, where, there being no dorsal arcs to tho somites of the pereion, the 

 legs appear to separate from the carapace or cephalon rather than from tho 

 pereion, of which they form an attached portion. 



The little animal clings to a fragment of weed or stone, and resting there 

 for a time, gradually liberates itself through the opening that I have de- 

 scribed, first by removing the whole of the body posterior to the cephalon, 

 then, after resting some short time, withdrawing tho head and its appendages 

 from the anterior portion. 



In the terrestrial forms, chiefly represented by the Ligia and Oniscus, 

 a variation in the exuviation appears to depend upon the nature of the 

 habitat ; thus, living in the air and creeping about among bushes, the worn- 

 out old epidermal tissue appears generally to be shed in portions, a circum- 

 stance that I attribute to the animal's surface coming into contact with 

 rough projectiug bodies, so ripping off portions before the whole is ready 

 to be cast off. In these creatures the new skin appears to have arrived at 

 a firmer and more resisting state before being shed than in the aquatic forms. 



When the Crustacea cast their old integument, and appear as renewed 

 animals, they exhibit afresh and uninjured all the appendages that have been 

 broken off or wounded. 



On Renewal of Appendages, 



It has long been known that these animals, after losing any of their ap- 

 pendages, have tho power of reproducing them. But the manner in which 

 this is done has been known only through the results of modern observations. 



The late Mr. H. Goodsir, in the 'Annals of Nat. Hist,' 1844, vol. xiii. p. 67, 

 writes, " That he has found that a small glandular-like body exists at the 

 basal extremity of the first phalanx in each of the limbs, which supplies the 

 germ of the future logs. This body completely fills up the cavity of tho 

 shell for the extent of about half an inch in length. Tho microscopic struc- 



F.2 



