100
Oesophagostomum radiatum
for the protection of the larva, the ecdysis being delayed till the larva reaches
the host. The body resembles that of the second stage in being nearly uni-
form in width and measures 0.820 to 0.885 mm. long including the tail and
.03 mm. broad. Of this length, the tail occupies about 0.208 mm. (Fig. 11).
The old skin or the sheath is somewhat loose and clearly shows the trans-
verse striations. The opening in the sheath corresponding to the mouth of
the larva is closed. The cuticle of the larva is newly formed beneath the sheath
and is also ringed. There are prominent lateral lines, one on each side and
correspondingly on the inside there are lateral bands projecting into the body
cavity.
The mouth is bounded by three lips which close it. There is a triradiate
cuticular design in the region of the buccal capsule. The buccal capsule is
extremely narrow and insignificant, and its length is reduced to 0.013 mm.
The œsophagus, 0.162 to 0.168 mm. long, and now of the strongyliform type,
does not show the three divisions in the first stage, though a slightly globular
portion may be observed at its posterior end without the Y-shaped valve.
About half its length, it is bent as a distortion. It is highly muscular with
transversely elongated cells, and is joined to the intestine by a valve composed
of two cellular rings.
The chyle intestine is usually built up of ten cells on each side, each cell
being roughly spindle-shaped, with a nucleus in the middle and richly laden
with granules. The passage is much compressed and zig-zag in appearance.
The rectal region runs aslant and ends with the anus which is occluded.
The excretory tubule leading out at a point 0.13 mm. away from the an-
terior end emerges from an assemblage of cells indiscernibly mixed with the
nerve cells.
Only in larvæ stained with Methylene Blue or Gram's Iodine can the
cephalic nerve-commissure be detected as a fibrous-looking band embracing
the œsophagus. Other nerve-units are arranged on either side of the anterior
section of the œsophagus ; behind the nerve-ring are the two lateral cephalic
ganglia indicated by two clumps of nuclei, and surrounding the rectum are the
nuclei of the anal ganglion.
The genital rudiment is larger than before 0.013 mm. long and is a com-
pressed oval mass of cells situated on the ventral side between the sixth and
seventh intestinal cells.
Biology.—The larva of this stage does not grow any further and is
the infective stage. The infective larva is extremely active and moves
gracefully after the fashion of a serpent. It evinces a definite migratory
tendency and journeys to a favourable locality where it could be picked
by the host. It commences such an activity, under normal conditions, at
the end of the fourth day and is captured in the water-jacket of the petri¬
dish culture sometime after. Many may even be caught in the act of
migration, by moving the tip of a moist camel-hair brush along the rim of the
small petri-dish containing the fæces. In the jar-cultures, these larvæ ascend
the walls of the jars in colonies, and in the open, they may be frequently found
to have migrated to the soil.
The sheath is very permeable, and on applying aqueous Neutral Red or
Methylene Blue it was discovered that the sheath alone absorbed the stain.