154 ANIMAL PARASITES AND MESSMATES. 



Mons. Krabbe in a dog which died of a disease to which 

 these animals are subject; it lived in the heart, and 

 twelve individuals, ten females and two males, were 

 found to be lodged there. Mons. Bap. Molin has pub- 

 lished a monograph on the Filariae, giving the characters 

 of 152 species met with in molluscs, fishes, amphibians, 

 reptiles, birds, and mammals : it seems evident that many 

 species have been confounded under the same name. 



A small worm, of the size of a slender pin, but much 

 shorter, lives in a manner somewhat analogous to that 

 which we have before described. It is known under the 

 name of Leptodera. In order to find it, we have only to 

 search in the woods for the first snail that we meet with, 

 which is distinguished by its orange or black colour : if 

 we prick with a pin the fleshy foot of the mollusc, we 

 shall see torrents of round worms come out, wriggling 

 like microscopic serpents. These worms also leave 

 their retreat, if we cause the foot to contract by touching 

 it with some acid, or if we place the snail in water. 

 The Leptoderse are especially remarkable for two fringes 

 which float by the side of their tail, which characteristic 

 suggested the name given to them by Professor Schneider. 

 These fringes so easily fall off, that the greater part of 

 those which have become free have none of these ap- 

 pendages. When placed in fresh or decaying animaJ 

 matter, in water or in damp earth, these wornis, 

 agamous when in the foot of the mollusc, rapidly 

 become sexual and perfect. Thus the snail serves them 

 as a creche, and the adult worm has no need of external 

 help when it has grown old. 



Professor Pagenstecher found at Ostend, on the 

 Nicotho'e of the lobster, nematodes which he arranged 



