In the first of these we will place together all those which are free at the commencement of their life, which swim and take their sport without seeking assistance from others, until the infirmities of age compel them to retire into a place of refuge. They live at first like true Bohemians, and are certain of getting invalided at last in some well-arranged asylum. Sometimes both the male and female require this assistance at a certain age; with others it is the female only, as the xx male continues his wandering life. In some cases, the female carries her partner with her, and supports him entirely during his captivity; her host nourishes her, and she in her turn feeds her husband. We find few female gill-suckers which have not with them their Lilliputian males, which, like a shadow, never quit them. But we also find males, living as parasites of their females, among those curious crustaceans known by the name of cirrhipeds. All the parasitical crustaceans are placed in this first category. We find others, the ichneumons for example, which are perfectly at liberty in their old age, but require protection while young. There are many of these, which as soon as they escape from the egg, are literally put out to nurse; but from the day when they cast off their larval robe, they are no longer under restraint, but, armed cap-à-pie, they rush eagerly in quest of adventure, and die like others on the high road. In this category are generally found parasitical hymenopterous and dipterous insects. Other kinds are lodgers all their lives, though they change their hosts, not to say their establishment, accordingly to their age and constitution. As soon as they quit the egg, they seek for the favours of others, and all their itinerary is rigorously traced out for them beforehand. Fortunately we are at present acquainted with the halting-places and magazines of a great number of those which belong to the order of cestode and trematode worms. These flat and soft worms begin life usually as vagabonds, aided by a ciliary robe which serves as an apparatus for locomotion; but scarcely have they tried to use xxi their delicate oars, before they demand assistance, lodge themselves in the body of the first host that they meet, whom they abandon for another living lair, and then condemn themselves to perpetual seclusion.