June is, 1914 
Citrus-Root Nematode 
227 
sive evidence on this point is the presence in the intestine of individuals of 
Mononchus of the remains of specimens of 
Tylenchulus. In several such cases no 
other ingested food appeared to be present, 
showing that the Mononchus had been 
making a meal on Tylenchulus. In 
searching for the remains of species of 
Tylenchulus in the intestine of a spe¬ 
cimen of Mononchus, one looks for the 
more indigestible parts, such as the oral 
spear and the spicula of the male (see figs. 
4 and 6). These being very indigestible 
and also highly refractive remain visible 
even when other parts of the Tylenchulus 
have been completely digested. 
This Mononchus is a relatively large 
species and, judging from this fact alone, 
would seem to be capable of devouring 
Tylenchulus semipenetrans in considerable 
numbers. These discoveries confirm those 
made earlier by the writer and render it 
certain that there is a class of beneficial 
nematodes inhabiting the soil. 
The pharynx of the active and preda¬ 
cious Mononchus is supplied with a promi¬ 
nent acute, dorsal, forward-pointing 
chitinous tooth. This tooth is opposed to 
six thick, muscular, hookshaped, back- 
acting lips, and it is by the interaction 
of these various organs that the Tylen¬ 
chulus is seized, punctured, and killed. 
Possibly the acute pharyngeal tooth of the 
Mononchus is nothing less than a poison 
fang, but this at present is only a matter 
of theory. It is, however, known that 
many nematodes have glands in the seg¬ 
ments of the oesophagus—the so-called 
oesophageal glands—and it is possible that 
these glands may secrete a poisonous 
liquid substance which may be used in the 
same way as the venom of serpents. Fur¬ 
thermore, the inner surface of the pharynx 
of the Mononchus is sometimes armed with 
scores of exceedingly minute rasplike teeth, 
which in some respects resemble, on a small rudimentary anus; », terminus, 
scale, those found in the pharynx of serpents and sharks, teeth which aid 
X500 
Fig. 13. —Tylenchulus semipenetrans: 
Young female about to undergo its 
second molt. Compare with figures 1 
and 6. Note that the spear in the 
growing female does not deteriorate. 
Note also the increasing size of the 
median or suction bulb of the oesopha¬ 
gus. Quite the contrary occurs in the 
male, a, Lip region; b , spear; b\ spear 
which has been sloughed off; d, lumen 
of the oesophagus; e, median oesopha¬ 
geal bulb; /, nerve ring; g, cardiac 
oesophageal bulb; h, beginning of the 
intestine; k , larger intestinal granules; 
n, excretory pore; n\ renette cell; o\ 
blind end of single immature ovary; 
r, developing uterus; V , remnant of 
