226 
Journal of Agricultural Research 
Vol. II, No. 3 
» 
uwM 
lMfci 
The original home of the cultivated species of Citrus is supposed to be 
India or southern China, and we may therefore suppose these lands to be 
also the original habitat 
of the Tylenchulus. 
The life history of Ty¬ 
lenchulus semipenetrans 
strikingly illustrates how 
little we know about or¬ 
ganisms inhabiting the 
soil. Here is an organism 
so large as to be visible 
to the naked eye, an or¬ 
ganism that, considered 
as a microscopic object, 
is relatively huge, occur¬ 
ring, practically speaking, 
in most parts of the world 
where Citrus fruits can be 
profitably grown, attack¬ 
ing and killing the roots 
of a crop of great eco¬ 
nomic importance. Yet 
this organism remained 
undiscovered for 200 years 
after mankind possessed 
instruments for its discov¬ 
ery. With such a striking 
instance before us, how 
can we doubt that thor¬ 
oughgoing biological soil 
researches will reveal a 
multitude of similar cases ? 
It is a common obser¬ 
vation among agricultur¬ 
ists that crops fail for 
some unknown cause. 
Such cases may appear 
less mysterious when we 
have an adequate knowl¬ 
edge of soil-inhabiting 
organisms. 
Not the least interesting 
feature of these investiga¬ 
tions into the life history of Tylenchulus semipenetrans has been the discov¬ 
ery of a species of Mononchus, another nematode, which regularly feeds 
upon the Tylenchulus * swallowing the males and the larvae whole. Conclu- 
Fig. 12 .—Mononchus papillatus Bastian: Rather immature female 
specimen which has been feeding upon Tylenchulus semipene¬ 
trans. The remains of three or four Tylenchuli are to be seen 
in the intestine, a , Two of the innervated papillae existing on 
one of the six mobile lips; 6, one of the lips; c, dorsal pharyngeal 
tooth; d , one of the three longitudinal chitinous ribs of the 
pharynx; e, pharyngeal cavity; /, oesophagus; g, muscular layer 
of the body; A, cuticle; j, one of the cells of the intestine; 
/, j, J, oral spears of three ingested Tylenchuli; the spear in the 
intestine near the vulva is accompanied by an undigested por¬ 
tion of the lumenof the oesophagus of the Tylenchulus; k , nerve 
ring; l, blind end of the anterior ovary, which, being behind the 
intestine, shows less clearly than the posterior ovary; m, nucleus 
of one of the intestinal cells; n t vulva; o, anus; p t terminus; q, 
anal muscles; r, rectum; s, cardia; t, spicula of an ingested male 
Tylenchulus. The outlines of the undigested tail end of the 
male are to be seen faintly. 
