We now come to an isopod which aims higher: he doubtless considers that cray-fish and crabs walk too slowly for him; he therefore addresses himself to a fish, the _Puntius maculatus_, which inhabits the river Tykerang (Bandong) in Java. This isopod is called _Ichthyoxenus Jellinghausii_. This isopod crustacean, living at first in the same manner as the rest, looks out for a small cyprinoid fish, thrusts itself like a trocar behind the abdominal fins, through the scaly skin, and penetrates entirely into the abdominal cavity. The male always accompanies its female. It is remarkable that she, in contradistinction to many others, preserves all the attributes of her sex. She does not change her form more than the other free crustaceans of her order, and only differs from the male in size. It is well known that in all these animals the male is always smaller than the female. Mons. Jellinghaus, who first described this crustacean, observed that all fishes which he caught had, without exception, the small ones 147 as well as those which were larger, a couple of these parasites in their stomach. We allude to it here, but we might as well call this _Ichthyoxenus_ a messmate as a parasite. On the coast of Brittany, among the many _Labri_, which are distinguished for their vivacity, and for the variety of their colours, is found a small species (_Labrus Cornubiensis_), on which is usually seen an isopod which is no less curious. It is constantly clinging to the sides of this fish, not far from the head, at the bottom of a hollow made under the scales. Naturalists have known this acolyte by Mons. Hesse's works. This _Leposphilus_ (for this is the name which has been given to it), though it does not prefer the scales to any other organ, forms a lodging for itself in the sides of this little Labrus, and takes up its abode there with its family. We cannot assert that it has chosen this refuge without any hope of returning, since both the sexes still keep their organs of locomotion. At the last congress of German naturalists at Wiesbaden, Dr. Kossmann, who has had the opportunity of examining the rich materials brought from the Philippine Isles by Professor Semper, gave an excellent account of the result of his careful observations on some other crustaceans still more remarkable, the _Peltogasters_ of which we have spoken before. In the course of this, he described an isopod with a development as completely recurrent as that of the peltogasters, whose rank among cirrhipeds is perfectly established.