98 ANIMAL PARASITES AND MESSMATES. 



each other in their external characters. What is not 

 less remarkable is, that hermaphrodite, worms often 

 unite in couples, and that only one of the two seems to 

 perform the function of a female, and increases in size 

 {Distoma Ohenii, Bilhartzia). It even happens that the 

 union is so complete that the species appears formed of 

 two individuals fastened to each other. The Diplozoa 

 show us a curious example of this. The gills of breams 

 are usually infested by these last-mentioned worms. 

 Nothing is more strange than to see all these individuals 

 united two and two as if soldered together, each pre- 

 serving its mouth and digestive canal, and producing 

 eggs which give birth to isolated individuals. We some- 

 times see males so completely absorbed in their females, 

 even in an anatomical point of view, that they only 

 represent a fragmentary apparatus. The male of the 

 Syngami is so obliterated, that when compared with the 

 other males of its order it is only a testicle living on 

 the female. 



Should an organ infested with worms be considered 

 diseased, simply on account of their presence ? We hesi- 

 tate not to say that, as long as these guests cause no 

 disorders, there is no pathological condition. The child 

 which has Ascarides liimhricoides in its stomach is not 

 necessarily ill. All animals in a wild state always 

 have their parasites ; they lose them rapidly when in 

 captivity. 



The Abyssinians do not take medicine when they 

 have taeniae ; on the contrary they are in a better state 

 of health. Do we not find medical men prescribing the 

 employment of leeches, and consequently calling in the 

 assistance of certain parasitical animals ? This action, 



