PARASITES FREE WHILE YOUNG. 139 



before choosing the host which is to serve them as a cell ; 

 but though in many species we see both sexes shut 

 themselves up as in a cloister, some species are to be 

 found in which the female alone seeks for extraneous 

 aid ; which is not surprising, since she alone undertakes 

 all the charge of the family, and this would be beyond 

 her strength, and would endanger the life of her off- 

 spring, if she did not receive help and protection. 



The host resembles in some respects a lying-in 

 hospital, especially when the female alone seeks for her- 

 self a resting-place and her food, which is hot always the 

 case. We find, in fact, in a considerable number of Ler- 

 naeans, that the microscopic male passes unperceived 

 upon his female, and when he renounces his bachelor 

 life, she feeds him with her own blood. There cannot 

 be a more faithful husband, since he only plays the part 

 of a spermatophore. We find a still more curious 

 example in this respect, and in which the dignity of the 

 male is not less compromised ; we refer to the Bonelliae 

 which live freely in the sand, and whose males establish 

 themselves parasitically on the sexual organs of the 

 female. She herself lives by her own industry, nourishes 

 her husband, and alone provides for all the requirements 

 of maternity. 



In a later part of this work, we shall mention worms 

 which live in freedom in damp earth, and whose direct 

 progeny, entirely composed of females and hermaphro- 

 dites, can only exist as parasites. These worms do not 

 resemble their mother but their grandmother, and if 

 their descent had not been traced, they would doubtless 

 have been taken for species entirely distinct from each 

 other. Thus it is not always the whole family which is 



