238 ANIMAL PARASITES AND MESSMATES. 



a good resume of the state of our present knowledge of 

 parasitical and wandering nematodes. 



The Sclerostomata are distinguished by their mouth 

 being surrounded by a horny armature. The river 

 perch usually gives lodging to a viviparous nematode, 

 the Cucullanus elegans^ on the development of which a 

 special work has been published. The young ones are 

 provided with a perforating stylet, and penetrate into 

 the bodies of small aquatic crustaceans, called cy clops. 

 When they have obtained entrance into this living 

 lodging, they bore through the walls of the intestines 

 and shut themselves up in the perigastric cavity. The 

 Cyclops being pursued by the young perch, are swallowed 

 with their guest, and the latter is set free in the midst 

 of the stomach, where it passes through its sexual 

 evolution. 



Leuckart saw in his aquarium young CueuUani 

 penetrate into the bodies of the cyclops. These crus- 

 taceans are therefore the vehicle of these nematodes. An- 

 other nematode worm, the Dochmius trigonocephalus, lives 

 at liberty while young, but seeks for an asylum in the dog 

 in its old age. The Sclerostomum equinum causes aneu- 

 risms in the horse, which manifest themselves by colic. 

 A hundred of these worms have been found in the same 

 horse. The Sclerostomum pinguicola is very common in 

 the pig in the United States. This is the Stephanurus 

 dentatus of Diezing, noticed by Natterer in Chinese pigs 

 in Brazil. Cobbold notices the same worm as living in 

 the pig in Australia; they have been also found in 

 Germany. 



The Strongyli are round, cylindrical worms, with 

 bodies sometimes entirely red, which inhabit different 



