ON THE NEMATODES OF THE COMMON EAETHWORM. 647 
whatever else its significance may be, the chitinous layer 
which lines the alimentary canal throughout must prevent an 
ingestion of bacteria by the endoderm cells themselves in such 
a way as Colpidium preys upon the bacteria of the soil.” 
The active nephridial larvae feed on the bacteria or bacterial 
products which pass down the nephridial tube in the current 
of coelomic fluid, or which may congregate in the dilated 
bladder-part. But the number of bacteria in the living worm 
must be relatively small compared with the number produced 
on its decay, and there is, thei’efore, little or no growth in 
this condition. Hence the larval period is a long one. But 
on the death and decay ot the worm large numbers of bacteria 
are produced, and, food noAV being plentiful, growth is rapid, 
and the nematodes mature and reproduce in a few days. 
Rhabditis pellio, then, not only belongs to a genus 
most of whose species are free-living, but in all respects except 
its habitat appears to behave like one of the free-living species 
of that genus. The role which Maupas (10, p. 623) ascribes 
to it when he speaks of it as “locataii’e inolfensif ” is the true 
one, and the advantages which it gains from its association 
with the worm are protection and dissemination. 
(2) Probable Course of the Life-Cycle. 
The results obtained in the foregoing investigation are not 
conclusive, but they suggest, I think, that the life-history of 
Khabd i ti s pel 1 io is somewhat as follows : 
When an infested Lumbricus terrestris dies in moist 
earth, the larvae of Rh. pellio which it contains feed on 
the nutriment afforded by its putrefying carcase, the encysted 
individuals emerging from their cysts. Growth is rapid. 
Within a week they develop into sexually mature males and 
females, and the latter reproduce. Reproduction is often — 
possibly always — hermaphrodite. But sometimes it seems to 
be bisexual. I am not certain whether in a natural state the 
body of the decaying worm is capable of affoi'ding sufficient 
nutriment for the production by these offspring, in their turn, 
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