CRUSTACEANS. 621 
cially Minne Epwarps, have made copious contributions to it, 
which however are confined principally to the order of the decapods. 
With the different peculiarities that have an influence on the distri- 
bution of species we are not yet satisfactorily acquainted. The 
difference of salt-particles in the different seas comes here beyond 
doubt into consideration, and not the mean temperature alone; the 
relative depth also, the nature of the coasts, &c. On the whole, 
the general rule, that animal forms, the genera and species, are 
more numerous in proportion as we advance from the poles to the 
equator, has not such an unlimited prevalence for marine animals. 
In size also and in brilliancy of colour the animals of the polar seas 
often contest the palm with those of the tropics. Yet the short-tailed 
ten-footed crustaceans, so rich in species in the seas of the warm 
regions of our globe, are almost entirely wanting in the neighbour- 
hood of the poles. On the other hand, the northern regions are 
rich in forms of amphipods, which necessitate the adoption of 
many distinct genera; so that the colder seas may be regarded as 
the proper home, the true father-land of these crustacea}. 
1H. Kroryer Naturhistorisk Tidsskrift, tv. 1842, pp. 141—166. On the geographic 
distribution of Crustacea compare LATREILLE Mém. du Muséwm, It. 1817, p. 453 or 
Mémoires sur divers sujets de UV Hist. nat. des Insectes, de Géographie ancienne, &e. 
Paris, 1819, Svo. p. 174; and especially MinnE Epwarps, Ann. des Sc. natwr. sec. 
Série, Tom. X. pp. 129—174. 
