ON CRUSTACEA. 267 



after a member is plucked away, a reddish pellicle is formed 

 upon the flesh, which is left exposed. Some days later, this 

 pellicle assumes a surface a little convex, it is elongated, be- 

 comes conical, still increases in size, and being cleft, leaves to 

 view a soft body, which is composed exactly of the parts 

 which are wanting to the member, but smaller in proportion 

 than those which remain. These new parts soon acquire 

 consistence; but it is not until after many moultings that 

 they acquire the volume of the old ones. It has been re- 

 marked, that this reproduction does not take place when the 

 member is broken between two articulations ; and it has even 

 been observed, that when this is the case, the Crustacea them- 

 selves tear out the remaining stump, so as to have the rupture 

 in the joint, where the new part can then be formed. 



The animals of this class compose but a limited assemblage 

 of species, but the individuals referrible to each of these species 

 are very numerous. They are met with in all latitudes, but 

 more abundantly, however, in warm and temperate climates 

 than in the frigid zone ; and their species are not indifferently 

 proper to all countries. Thus the amphipod and isopod Crus- 

 tacea seem to be more peculiarly the inhabitants of the 

 colder regions of the globe, while the decapods are more com- 

 mon between the tropics. In the medial zones we observe a 

 mean proportion of the species of these different orders. 



Certain genera, such as the ocypods, gecarcinus, gelasimus, 

 uca, hippa, limulus, grapsus, &c. are found in more southern 

 latitudes than the others, pretty nearly under the same paral- 

 lels, on the American, Asiatic, and African shores ; others, on 

 the contrary, such as the crabs proper, portunus, and inachus, 

 occupy more space, and are extended even to the polar cir- 

 cles. 



As to the small entomostraca, they have as yet been ob- 

 served only in temperate countries ; but there is reason to 



