The common "Freshwater Shrimp" (_Gammarus pulex_), which has already been described, may be taken as a type of a large number of Amphipoda, for the most part closely allied, which are widely distributed in most regions of the world, with the exception of the tropics. _G. pulex_ itself ranges from the British Islands to Mongolia. As the eggs are carried, till they hatch, in the brood-pouch of the parent, and are not known to survive drying, it is difficult to understand in what way _Gammarus_ and its allies contrive to spread from one locality to another. The little fresh-water Isopod _Asellus aquaticus_ (Fig. 60) is common in ponds and canals in this country. It may be recognized by its general resemblance to a Woodlouse, with very long antennæ, and with a pair of long, slender, forked uropods projecting behind. The species is widely distributed in Europe, and other species of the same and closely related genera are found in North America. [Illustration: FIG. 60--_Asellus aquaticus_, FEMALE. × 4. (After Sars.)] In Australia and New Zealand the Isopoda are represented in fresh waters by a very peculiar group of species, forming the suborder Phreatoicidea, which have more the aspect of Amphipods than of Isopods, since the body is more or less flattened from side to side, instead of from above downwards. With regard to the mode of distribution of the fresh-water Isopoda, there is the same difficulty as in the case of the Amphipoda, for the eggs are carried in a brood-pouch, and do not seem to be in any way protected against drought. It is no doubt in consequence of this that the fresh-water species and genera of both Amphipoda and Isopoda, though widely distributed, do not have the world-wide range of many of the more minute Crustacea described above.