22 EARTHWORMS AND LEECHES [CH. I 



constantly be found quantities of parasitic Nematodes (or 

 thread-worms). These are the Rhabdites larvas of Pelo- 

 dera pellio, they do not become mature until they pass 

 into the earth after the death of their host. Probably the 

 young enter the worm through the mouth with food, but 

 the life-history is not known with certainty. 



R. Leuckart has described a species of A scar is which 

 lives free within the muscle fibres of the mole. The 

 parasite has a well-marked boring tooth. Leuckart 

 mentions that earthworms are infested by an Ascaris of 

 similar appearance, and with a similar tooth. When eaten 

 by a mole the young Ascarids of the earthworm are said 

 to be destroyed by digestion. But when infected mole's 

 flesh was eaten by a buzzard, the lungs and liver of the 

 bird became covered with tubercles containing the young 

 Ascarids, in the same stage of development as in the 

 muscles of the mole. It is obvious that the life-history of 

 this parasite requires re-investigation. Dujardin in 1838 

 and 1839 found in the " testicules " (vesiculce seminales) 

 of earthworms taken in Paris a Nematode which he 

 named Discelis filaria ; he described it as being white, 

 thread-like, from 3 to 5 mm. long, blunt at the extremities ; 

 skin with faint transverse striations; tail with two disc- 

 shaped suckers laterally. Dujardin subsequently failed 

 to find this parasite among earthworms elsewhere, nor 

 have they been since reported by other workers. In the 

 ventral blood vessel of the earthworm occur, as first de- 

 scribed by Cori, larval Nematodes, which von Linstow 

 recognised as the immature forms of Spiroptera turdi, 

 found as parasites in the coats of the stomach of the 

 thrush, blackbird, redwing and some other birds, in which 



