190 ANIMAL PARASITES AND MESSMATES. 



to seek. These investigations have already yielded the 

 best results in the laboratories of Giessen and of Leipzic, 

 under the direction of Leuckart. 



The genealogy of the distomidae is as follows : the 

 young distome, when it leaves the egg, is wrapped in a 

 ciliated tunic, and, under the guise of a microscopic in- 

 fusorial, it abandons itself to all the vagaries of a free 

 and vagabond life ; this is the bright period of its life. 

 "It is a youth starting, with all the steam up, without 

 help and without guidance, in the midst of the ocean ; if 

 it meets an island on its passage, that is to say, the body 

 of an aquatic larva or a mollusc, it disembarks, brings 

 forth its young, and disappears ; its purpose is fulfilled. 

 If it find no island or continent it sinks and perishes, 

 for it carries no provisions with it ; it has no organ which 

 permits it to take nourishment on its passage." If life is 

 short, even in the case of a young distome, it is passed in 

 the midst of the water : if fortune is favourable to it, it 

 will at last meet with a living abode, where it will find 

 all that is necessary to the comfort of a parasite. 



Abundance always reigns in these living oases ; and 

 as these new colonists are really exiles, who will never 

 again see their native country, ciliary oars are useless to 

 them, and their descendants difi"er entirely from their 

 common mother. 



Under the ciliated tunic of the mother appears a 

 daughter under the form of a bag, who is born almost 

 at the same time as herself, and concerning whom we 

 may quote here the words of Eeaumur : " Singular and 

 mysterious duality in unity ; two beings, living one 

 within the other, which are still only a single individual. 

 Has nature accustomed us to such profusion ? Do we 



