268 SUPPLEMENT 



believe that, from the degree of temperature necessary to their 

 existence, they abound in the fresh waters of warmer cli- 

 mates ; while, on the contrary, they are very rare, if even they 

 exist at all, in the very northern regions. 



The local habitations of the Crustacea, considered generally, 

 are very various : the most numerous of these animals are 

 aquatic and marine, and some few genera, such as oniscus, 

 armadillo, &c. are alone truly terrestrial. Certain brachyur- 

 ous decapods penetrate very far into the land, but are forced 

 to re-enter the sea at the period of coupling and laying. 

 Some others, such as thelphusa, though they have forms very 

 analogous to those of the marine crabs, do not quit the fresh 

 water, and all the entomostraca, except limulus, caligus, and 

 some animals approximating to the last, are also inhabitants 

 of fresh water only. 



Among the marine species, the majority do not quit the 

 shores, while others live in the high seas, and have nothing to 

 repose on but those floating banks of sea-weed so abundant 

 between the tropics. Moreover, the littoral Crustacea do not 

 all sojourn in similar localities: some, as dorippus, and certain 

 inachi, reside at depths of from two to four hundred feet, while 

 others continually sport on the surface of the waters, and pass 

 one half of their existence on the shore, which is continually 

 washed by the waves. Many species are met with only in 

 rocky situations, abounding in madrepores, and of difficult 

 access ; while others seek the bottom of the fine and shifting 

 sand, into which they sink themselves. 



Among those which come to laud and make a tolerably long 

 sojourn there, many brachyurous Crustacea (the ocypods) 

 excavate tolerably deep burrows, at the entrance of which 

 they usually remain on guard. Some (the ranini) are said 

 even to climb on elevated places, and often to mount on the 

 roofs of the Indian cabins 



