pair of legs in the female, and the fifth pair of legs in the male (Fig. 88). The eggs are carried on the swimmerets.
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Fig. 89.—Level lengthwise section showing
h, heart.
d, green gland.
le, liver.
kie, gills.
kh, gill cavity.
ma, stomach.
(After Huxley.)
Internal Structure.—Suggestions. If
studied by dissection, it will be necessary
to have several crawfish for each pupil, one
for gaining general knowledge, and others for
studying the systems in detail. Specimens
should have lain in alcohol for several days.
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Fig. 90.—Section of Crawfish showing stomach s, liver li, and vent a.
The Food Tube.—Is the stomach in the
head portion of the cephalothorax or in the
thoracic portion? (Figs. 88, 89). Is the stomach
large or small? What is its general shape?
Does the gullet lead upward or backward?
Is it long or short? (Fig. 88.) The mid tube,
which is the next portion of the food tube, is
smaller than the stomach. On each side of
it are openings from the bile ducts which
bring the secretion from the digestive gland,
sometimes called the liver. Does this gland
extend the whole length of the thorax? Is
it near the floor or the top of the cavity?
The third and last portion of the food tube
is the intestine. It extends from the thorax
to the vent. Is it large
or small? Straight or
curved? The powerful
flexor muscles of the tail
lie in the abdomen below
the intestines. Compare
the size of these muscles
with the extensor muscle
above the intestine (Fig.
90). Why this difference?
Does the food tube extend
into the telson? Locate
the vent (Fig. 90).
