G46 
GILBEET E. JOHNSON. 
they do not recover from the conditions of diminished vitality 
under which they have been existing'. Those which emerge 
are therefore the more recently encysted ones, which have not 
yet begun to degenerate. 
(8) Nature of Food. — Rhabditis pellio belongs to 
a genus, most of whose members are free-living in the soil 
and mature and reproduce on animal or vegetable substances 
in putrefaction. It resembles these in the conditions under 
Avliich it matures and reproduces. But it differs from them 
in spending all or part of its larval period in the body-cavity 
of an animal instead of in the soil. It does not appear to do 
any damage to the worm. It occurs in the largest and 
healthiest-looking individuals in quite as large numbers as in 
weakly specimens. Moreover, having, like all the species of 
the genus Rhabditis, an unarmed buccal cavity, it is 
incapable of feeding on the tissues of the living Avorm. 
Its food consists of liquids, Avhich are taken in by the suc- 
torial action of the oesophagus. It groAvs most rapidly in 
)uedia Avhich are swarming Avith bacteria, which shows that it 
is upon the bacteria or the products of their action that it 
lives. What Potts says of the free-living species of the genera 
Rhabditis and Diplogaster applies to this species also. 
He says (15, p. 444) : “It is only in the presence of great 
numbers of bacteria, or the substances formed by them, 
that the nematodes thrive so well. ... It has not been 
discovered Avhether digestion takes place by the secretion of 
juices dissolving the protoplasm of the bacteria, or is merely 
confined to the absorption of soluble substances present in the 
culture fluid and prepared by the action of bacteria. 
An easily observable phenomenon of nematodes in culture is 
the rapid pumping action of the second CESophageal bulb and 
the rectum, and it may be argued from this that the nutri- 
ment obtained from the stream of fluid so constantly passing 
through the alimeutary canal is in the form of easily abstracted 
soluble substances. The insignificant development of glan- 
dular cells (which are found only in the oesophagus) may be 
cited against an intra-intestinal digestion of the bacteria, and, 
