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Oesophagostomum radiatum
The mouth is a narrow aperture at the rounded anterior end and leads
into a short buccal cavity, 0.01 mm. long and which could be distinguished
as two dark parallel lines. This is continued as the œsophagus, which is typi-
cally rhabditoid in structure divisible into three regions, an anterior thickened
muscular region of a thickess of 0.008 mm., a middle narrow one 0.003 mm.
wide and a posterior bulbous region of 0.01 mm. Each section passes on
to the next insensibly. The walls of the œsophagus are highly muscular, the
cells which have prominent nuclei are arranged in rings and lend a striated
appearance to the organ, and the lumen of the œsophagus is of a fine calibre.
In the middle of the bulb is the characteristic Y-shaped valve.
The next and the longest section of the digestive system is the chyle
intestine extending to the rectum. The junction between the œsophagus and
the chyle intestine is represented by two rings of cells which in an optical
section appear as two nucleated cells, one behind the other on each side.
The cavity of the intestine, wide at the œsophageal end, follows an undulat-
ing course till the end caused by the alternate projection of the cells on its
wall. The cells are eight on each side, each with a large nucleus, and measur-
ing 0.025 × 0.005 mm. roughly pyramidal, and densely granular in this stage,
which feature causes them apparently to merge into one another.
The rectum is disposed obliquely, short, measuring 0.016 mm. in length,
and passing through a cluster of cells to open as the anus on the ventral surface.
The anus is located 0.31 mm. from the anterior end.
Also opening on the ventral side but much anteriorly, 0.07 mm. from the
oral end, is the excretory canal, extremely narrow and fine. It curves inside
and disappears amidst a collection of cells below the bulb of the œsophagus.
The nerve elements of the larva are not easily observed unless the larvæ
have been stored for sometime when they become clearer. Encircling the
middle region of the œsophagus is a ring of nerve-fibres constituting the cepha-
lic commissure with a width of 0.004 mm. In the vicinity of this band of
nerve are groups of separate cells which are associated with the nervous system.
Another cluster of similar cells through which the rectum passes is identified
to be the primordium of the anal ganglion.
The genital anlage is an oval mass of two compacted cells, measuring
0.006 mm. and situated on the ventral side, between the 4th and 5th cells
of the chyle intestine, 0.098 mm. anterior to the anal aperture.
Biology. The first-stage larva is seen to move slowly by lashing its
tail and wriggling in the water, but does not cover any considerable
distance even in its active moments. It never leaves the fæcal mass
in which it develops, except when it is observed inside the excremental
pellets whose outside has dried or on the superficial layers of the soil in
contact with the fæcal mass. There appears to be voracious feeding in
this stage and building up of reserve food. The oral end is persistently
busy with the intake of food. The resistence of the larva to temperature
and desiccation is extremely limited as in fæces exposed to the atmosphere,
numerous larvæ are discovered dead in the dried regions.
This stage normally lasts for about 24 hours and during this period, a
physiological distinction into two sub-stages is recognized. The first is a sub-