and Ilhisfrations in Natural History. 257" 



into a new form : " a form in which its members were 

 changed in number as well as in proportion and figure ; for 

 they had lost the structure which fitted them for swimming 

 in the bosom of the sea, and had assumed that of the crab, 

 destined to creep henceforth on its bottom. In May, 1827, 

 a similar experiment was made with similar results ; and, soon 

 afterwards, the zeal of this excellent naturalist was rewarded 

 by a satisfactory proof of his discovery, he having, after nu- 

 merous fruitless attempts, succeeded in hatching the ova of 

 the common crab ; and witnessed issuing from them the fcetal 

 young, in the similitude and guise of Zoea Taurus, with the 

 addition only of lateral spines to the corselet. We think the 

 inference a fair one which extends a similar metamorphosis 

 to all the similar Decapodous Crustacea ; which, consequently, 

 in their first and tender stage, must be " essentially and purely 

 natatory animals, and, no doubt, possessed of corresponding 

 habits, swimming about freely, and without intermission, in 

 search of appropriate food. In their perfect state, the greater 

 number can no longer avail themselves of the power of swim- 

 ming, but are furnished with pincers and feet almost solely 

 adapted to crawling; so that they are now under the neces- 

 sity of confining their excursions in pursuit of prey within 

 more narrow limits. This curious piece of economy explains 

 what has ever appeared paradoxical to naturalists, viz. the 

 annual peregrinations of the land crabs to the sea-side; 

 which, although acknowledged to be true by several compe- 

 tent observers, could never before be satisfactorily accounted 

 for." (p. 9.) 



The opossum shrimp (Mysis Latr.) forms the subject of 

 the next memoir, which is full of interest. These Crustacea 

 abound in the arctic seas, where they afford much food to 

 the whale ; and we are told that they are the most common of 

 their class on our own coasts, where, in estuaries particularly, 

 they may be observed forming an almost continuous band or 

 column of some feet in breadth, extending ^ong either mar- 

 gin of the tide, from the sea up to where ^Ire water becomes 

 almost fresh. In appearance they are not unlike a small 

 shrimp, but the Myses have four rows of legs, eight in each 

 row ; or, more properly speaking, each leg is divided to its 

 very origin into two parts or limbs, the inner limb being con- 

 structed for progression and the seizing of their prey, and the 

 outer one for swimming and the giving of that motion to the 

 water which is essential to the respiratory organs, which are, 

 as it were, wrapped around the base of this limb, and fully 

 exposed to the action of the ambient fluid. The little crea- 

 tures swim easily, with a curved back and drooping tail; 



Vol. IV. — No. 19. s 



