INTBODUCTION. 



male and female require this assistance at a certain age; 

 -with others it is the female only, as the 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 pro- 

 tection 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-a-pie, they rush eagerly in quest of adven- 

 ture, 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^ ac- 

 cordingly to their age and constitution. As Boon as they 

 quit the egg, they seek for the favours of others, and all 

 their itinerary is rigorously traced out for them before- 

 hand. 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 trema- 

 tode worms. These flat and soft worms begin life 

 usually as vagabonds, aided by a ciliary robe which 



