In some few cases, indeed, among the shark and ray family, the mechanism for protection goes a step or two further than in these simple kinds. That well-known frequenter of Australian harbours, the Port Jackson shark, lays a pear-shaped egg, with a sort of spiral staircase of leathery ridges winding round it outside, Chinese pagoda wise, so that even if you bite it (I speak in the person of a predaceous fish) it eludes your teeth, and goes dodging off screw-fashion into the water beyond. There's no getting at this evasive body anywhere; when you think you have it, it wriggles away sideways, and refuses to give any hold for jaws or palate. In fact, a more slippery or guileful egg was never yet devised by nature's unconscious ingenuity. Then, again, the Antarctic chimaera (so called from its very unprepossessing personal appearance) relies rather upon pure deception than upon mechanical means for the security of its eggs. The shell or case in this instance is prolonged at the edge into a kind of broad wing on either side, so that it exactly resembles one of the large flat leaves of the Antarctic fucus in whose midst it lurks. It forms the high-water mark, I fancy, of protective resemblance amongst eggs, for not only is the margin leaf-like in shape, but it is even gracefully waved and fringed with floating hairs, as is the fashion with the expanded fronds of so many among the gigantic far-southern sea-weeds. A most curious and interesting set of phenomena are those which often occur when a group of fishes, once marine, take by practice to inhabiting freshwater rivers; or, _vice-versa,_ when a freshwater kind, moved by an aspiration for more expansive surroundings, takes up its residence in the sea as a naturalised marine. Whenever such a change of address happens, it usually follows that the young fry cannot stand the conditions of the new home to which their ancestors were unaccustomed--we all know the ingrained conservatism of children--and so the parents are obliged once a year to undertake a pilgrimage to their original dwelling-place for the breeding season.