258 ANIMAL PARASITES AND MESSMATES. 



splits on the back, so that the skin remains fixed between 

 the larva of the parasite and that of the wasp. It then 

 sucks the rest of the juices of the young wasp, and 

 becomes a nymph in the prison which it has formed for 

 itself. This evolution lasts from twelve to twenty-four 

 hours. 



Many male crustaceans, though they differ materially 

 from their females in form as well as in manner of life, 

 do not remove far from their partners in order to procure 

 the assistance which they need. The insects which 

 now occupy our attention are entirely different in this 

 respect. The male preserves his usual appearance 

 during the whole of his life, as well as the attributes 

 and independence of free insects; while the female 

 seeks for assistance with regard both to food and lodg- 

 ing from the time she leaves the egg; she is still 

 wrapped up in swaddling clothes when she receives the 

 male, as when she came forth from the egg. 



The worms of this category are usually fully formed 

 without undergoing metamorphoses ; and if the place 

 which they choose at their exit from the egg is not pre- 

 cisely their cradle and their tomb, at least all the phases 

 of their monotonous life occur around it. They may 

 be ranked among the most beautiful and the largest of 

 parasitical worms ; and as they are hermaphrodites, we 

 find no greater diversity in the several forms than in 

 their differences of age. All have their reproduction 

 certain, and their eggs are less numerous for this reason. 

 There are some of them that lay only one egg at a time, 

 and this egg sometimes appears but once during a 

 season. This explains why the eggs of some of these 

 worms have not yet been recognized. 



