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when the worm has reached its most extended state. They are not found in the
larval stages.
The significance of these vesiculæ probably is to facihtate the movements and
invasion of the worm into the mucuous membrane of the stomaeh of the rat. Its
way of moving the front part by extending it as much as possible and after-
wards contracting it violently, might support this theory, at any rate there is a
great resemblance between this way of moving and the one known from the earth
worm.
The front part of the nematode is devoid of real Kps. The mouth has the shape
of an equilateral triangle the edges of which are very easily moved forwards and
backwards, and used incessantly during the moving of the worm. This faet may
be observed most distinctly in the larva, escaped from its capsule in the muscles of
the cockroach. At this stage of development the front part in all essentials has the
same aspect as that of the fuUy developed nematode. When freed from its capsule
the larva appears exceedingly agile, moving constantly onwards in search of spots
suitable for intrusion.
The worm being placed into a solution of physiological common salt the move-
ments of its front end may very easily be studied under the microscope: it bends it-
self into all directions protruding and retracting incessantly the lip-shaped edges of its
mouth.
It has not been possible to decide with certainty whether papillæ may be found
in this species or not; some have been met with, but they were rather inconspicuous,
and even under high magnifying power (Zeiss Apochr. 2 m. m.) they were not con-
stantly observed in the different individuals. Just under the ridge due to the edges of
the mouth a laterally placed very small warty papilla was observed.; it is also to be
seen in fig. 18; but as before said it has not been found in all individuals. The
cervical papillæ, characteristic of Gongylonema are entirely absent.
In the same fig. a little lower down and sublaterally placed, some jagged lines are
found, passing obliquely upward and inward. They are very unequal as far as their
distinctness is concerned. They seem to be very low, list-shaped ridges, most promi-
nent in such spots as in the fig, present the triangular point. It may be that the
latter presents a sublateral papilla, the shape of which then differs from that of the
laterally placed papilla, mentioned above.
The lateral bands are easily perceptible passing throughout the length of the
animal. In the male they reach the width of c. 60 [jl\ in the female, however,
a width of about twice as much. They are sharply marked against the muscu-
lature and divided into 2 side halves, through the middle of which is seen a single
row of very small but distinct nuclei (see fig. 22). These are placed very regu-
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