ON THE NEMATODES OP THE COMMON EAETmVOEM. 649 
This passing backwards and forwards between the body of 
the worm and the soil may have interesting consequences when 
it takes place during the detachment of the cocoon of a worm 
engaged in reproduction. The finding’ of larval nematodes 
within the closed cocoon suggests that, when the latter is 
being slipped forwards towards the head, some of the nema- 
todes in the nephridia pass out into the cocoon through the 
uephridiopores. But the young worm in the cocoon has not 
been found to be infected, and the inference is that tlie 
presence of the Jiematode is only accidental, and that, when 
the young worm hatches out of the cocoon, the nematode 
escapes into the soil. 
Summary or Principal Eesults. 
(1) The active larval nematodes inhabiting the nephridia 
of the common earthworm, Lumbricus terrestris Linn., 
and the encysted larvae found in the coelom of the same host 
belong to the same species of Rhabditis. 
(2) This species I regard as distinct from Rhabditis 
pellio Schneider, with which it has hitherto been confused. 
Biitschli first described it but regarded it as merely a form 
of Rh . pellio. Rh. pellio is, however, a soil species which 
may mature on decaying earthworms ; the species described 
in this paper is a parasite of the earthworm and has not 
hitherto been recorded with certainty in the soil. I propose 
to designate it provisionally by the name Rhabditis pellio 
Biitschli, non Schneider. 
(3) The dimensions attained by the adults of this species 
vary considerably according to the nutritive value of the 
culture medium employed. Decaying earthworm, the food 
material on which the species grows to sexual maturity in a 
natural state, has been found more nutritious than the usual 
artificial media, such as peptone, and promotes correspondingly 
greater growth. 
(4) A medium consisting of extract of earthworms has 
