116
Oesophagostomum radiatum
The mouth is open and bounded by three lips, each of which is a triangular,
leaf-like structure with a pointed tip. In some specimens these were observed
to be apposed together to close the oral aperture. There is a very short and
narrow buccal capsule, whose sides are not so heavily chitinised as before.
The œsophagus is 0.16 mm. long, still of the strongyliform type, with a
claviform shape ; the bend in the middle which was present in the previous
stage has disappeared. The posterior portion of the œsophagus is gradually
swollen and rounded. The cavity is reduced to a great extent, and the walls
are thick and striated. The intestine is the most significant region of the
alimentary system and fails to reveal its cellular organization. It is densely
filled with granules and globules, has almost parallel sides and an irregular but
definite cavity. It extends 0.52 mm. from the œsophagus, to join the rectum.
The rectum is wide where it meets the intestine, with two symmetrical out-
growths on its walls, the rectal ligaments. Therefrom it runs obliquely towards
the body-wall and opens to the outside as the anus. The excretory tubule,
opening out 0.07 mm. from the oral end, is the outlet for the materials excreted
by the two large cervical glands lying free in the coelom on the ventral side.
In Fig. 13, the larger of the two appears as a fusiform, granular and nucleated
mass over the anterior region of the intestine and extending beyond the middle
of the body. In front it tapers into a narrow neck which is continued as the
excretory canal.
The nervous system is constituted of a ring of nerve-fibres encircling the
œsophagus in the vicinity of the excretory pore, and numerous nuclei on either
side of the posterior half of the œsophagus.
The primordial genital rudiment has increased in the number of cells and
in its length. It measures 0.025 mm. long and is placed ventrally and close
to the intestine 0.2 mm. from the anal aperture.
The fourth-stage larva
The third-stage larva inside the nodule grows rapidly and after an ecdysis
between four and five days from the time of ingestion passes to the fourth-stage.
The discarded sheath may be invariably seen in sections of the cyst in the
nodules. The larvæ described as being the intra-nodular stage by Marotel
[1908] and subsequently by Monnig [1933] belong to this latter stage. A
short account of the significant features of the fourth-stage intra-nodular larva
of O. columbianum is given by Veglia [1923], and the corresponding stage of
O. radiatum does not differ from the former in any respect except the size.
The length of the larva (Fig. 14) varies from 2.35 mm. to 2.5 mm. and
the larva is frequently in the uncoiled condition. The mouth is broad and
bounded by chitinous lips, six in number. The buccal capsule which had
hitherto been narrow and linear has transformed into a spherical, ankylostomi¬
form or cupoliform cavity, 0.05 mm. in diameter and with a heavily chitinous
wall. This should be regarded as a provisional capsule, uniformly observed in
all the fourth-stage larvæ of Oesophagostomum. At the base of this capsule and
projecting anteriorly from the chitinous doral wall is a solitary blunt tooth.
From this point starts the œsophagus measuring 0.32 mm. in length, and
0.07 mm. in breadth posteriorly. The walls of the œsophagus are thick