M.
ANANTARAMAN
97
stage of intense activity when the larva feeds and prepares for further growth
and extends to nearly 12 hours after hatching. All on a sudden, the larva
discontinues its movements and undergoing drastic changes lies extended and
apparently lifeless. It is not unusual to mistake such larvæ for dead ones
but their true condition may be judged by their unwilling movements when
disturbed in water on a slide. This lethargic state involves a metamorphosis
of the larva into the next stage. All the organs appear faint, the intestinal
cells lose their outline and the lumen is not so conspicuously wavy as before.
The purpose of this lethargy is fulfilled when a new skin with its lateral lines
is differentiated as a striated layer below the existing one, the œsophagus is
bent about its middle and the intestinal cells are increased in number. At the
termination of this lethargy, say 12 hours, these characters become pronounced
and after an ecdysis, the larva is roused from sleep.
The second-stage larva
The ecdysis, now occurring for the first time in the life of the worm amounts
to the discarding of the old skin and heralds the transformation to the next
stage. The larva inside the skin has already in its lethargic state acquired
the characters of the second-stage and soon after this unveiling, it is stimulated
to feeding and locomotive activities. The ecdysis is not achieved in an en-
tirely fluid medium as, when first-stage larvæ are left in distilled water, they
do not moult. A medium that would offer resistence, such as agar, is neces-
sary. The larva could also liberate itself from its old skin by piercing solid
fæcal masses in a fæcal emulsion, when the skin is held by the fæcal particles
on its sides and the larva emerges at the anterior end. The unwanted sheaths
may be observed in agar cultures, lying free and collapsed.
There is a marked increase in the length of the larva which is now calcu-
lated to be about 0.63 to 0.70 mm. by 0.02 to 0.025 mm. and as also other
structural changes typifying this stage (Fig. 10). The buccal capsule is
narrower and 0.015 mm. long. The œsophagus is looped about its middle
and is not so rhabditoid as in the first stage, the bulbous region being less
conspicuous. The Y-valve appears distinct. The cells of the intestine are
densely laden with granules, are flattened and count nine on each side. The
undulation of its lumen is less deep than before. The lateral lines are promi-
nent and thick and have flat edges. The nerve-ring surrounds the œsophagus
in its looped region, the excretory canal is 0.088 mm. away from the mouth
end, and the genital primordium is composed of two cells and of 0.01 mm.
in length, and implanted between the fifth and sixth cells and 0.175 mm.
in front of the anus.
Biology. The serpentine movements are very energetic and the feeding
continuous. The larva resembles the first stage larva in not attempting
to desert its place of birth and in its feeble resistence to temperature,
dryness, etc.
The span of life of this stage is approximately 50 hours, so that at the end
of it (i.e. about 86 hours after the egg is expelled with the fæces) the next
stage is reached. The two sub-stages of activity and lethargy are quite as
distinct as in the previous stage. The period of inactivity commences about