PARASITES FREE WHILE YOUNG. 157 



eggs ; we refer to the Ascaris nigro-venosa, the prin- 

 cii^al characters of which have been made known by 

 Professor Leuckart. This Ascaris is a true parasite, 

 which, when it arrives at its destination, where it finds 

 lodging and . food, leaves the lungs to go and inhabit 

 another organ. There is nothing surprising that certain 

 worms pass fi'om the intestines to the stomach, mount 

 thence to the oesophagus, and sometimes come out of the 

 mouth ; but here we have decided changes of abode in 

 the same animal ; that which shows, besides, that it is 

 not a simple accident, is that the animal is of a different 

 sex according to the apartment which it occupies ; here, 

 it is hermaphrodite, there it is male and female. The 

 Linguatulae, indeed, migrate from the peritoneum of the 

 rabbit to the nasal fossae of the dog : but the Ascaris 

 nigro-venosa first lives in the lungs of the frog, then goes 

 to inhabit the rectum of the batrachian, or damp earth. 

 In the lungs it is very sn.:il and viviparous, and pro- 

 duces young ones which become stronger than their 

 parents. The generation which live in the lungs are 

 hermaphrodite, the others are dioecious ; that is to say, 

 !.he males and females have hermaphrodites for their 

 parents. We have thus a mother, a simple female or 

 hermaphrodite, very small, which produces, not eggs 

 but young ones fully formed ; and instead of living, like 

 the mother, in the lungs, and breathing there with 

 greater or less facility, they go and lodge in the rectum, 

 and become, not like their mother, \dviparous and herma- 

 phrodite, but oviparous and of separate sexes. They 

 produce in their turn a race of giants, and instead of 

 following the example of their father or then mother, they 

 all go and lodge in the lungs like their grandmother. 



