606 
GILBEET E. JOHNSON. 
are enclosed in cysts or capsules, by which movement is 
restricted or entirely prevented. Those inhabiting the 
nephridia, on the other hand, are free and active. The en- 
cysted, coelomic form has long- been known as Rhabditis 
pellio, having been named by Schneider ( 1 ) as early as 
1866. The nephridial form is generally believed to be the 
same species, but it was not mentioned by Schneider, and I 
have not been able to find that its identity has been deter- 
mined by any subsequent investigator, as the following brief 
survey of the literature will show. 
In 1845 Dujardin, according to Bastian (2), recorded the 
existence of nematodes in the general body-cavity of the 
earthAvorm. These he placed in the genus Rhabditis. He 
found that they developed in prodigious numbers, forming 
whitish masses in the vessels in which he had kept earthworms 
with moss and damp soil. Bastian says that Dujardin also 
described a nematode, Dicelis filaria, occurring in gi’eat 
abundance in the nephridia of the earthworm. 
In 1858 Lieberkiihn, according to von Linstow (3), shoAved 
that the “Pilariae of the earthworm,” after the death of 
their host, creep out of the cysts, moult, and in a feAv days 
develop into mature Avorms. 
In 1864 and 1865 Lankester (4, 5) mentioned the nema- 
todes as occurring in the lobes of the seminal vesicles, in the 
posterior end of the coelom and imbedded in the muscular 
layer of the body-wall. 
Hitherto only the larvae had been investigated, but in 1866 
Anton Schneider ( 1 ) described the adults. He stated that 
they occur “in damp earth and putrefying substances.” 
These terms he must have used to signify dead eartliAvorms 
decaying in moist earth, for he says — “ The larvae occur 
encysted in the body cavity of eartliAvorms, especially on the 
septa,” and adds that, as Lieberkiihn was the first to point 
out, they become sexually mature on the decay of the Avorms. 
Schneider named the species Pelodera pellio. 
In 1873 Biitschli (6) described the adult males and females 
obtained from decaying earthworms in greater detail and Avith 
