MOLTING 
61 
these are fin-like and by their constant waving motion 
serve to carry food to the mouth. Others are elongated 
and serve for walking. One pair, the pincers, are used 
for seizing and holding food. 
The last abdominal segment and the appendages next 
to the last are broad and form a tail fin (caudal fin). 
Molting. — One of the interest¬ 
ing features in the study of the 
crayfish is the shedding of the ex¬ 
ternal skeleton. Being covered by 
a firm exoskeleton it is necessary 
that this be removed occasionally, 
in order that the animal may grow. 
Molting, in the case of the crayfish, 
is a serious and dangerous opera¬ 
tion, as it is followed by a period 
during which the crayfish is without 
means of offense or defense. The 
crayfish usually hides until a new 
exoskeleton is partially formed. 
In the molting process the cover¬ 
ing of the eyes and part of the lin¬ 
ing of the digestive tract, as well as 
the whole exoskeleton, are shed. The crayfish molts every year 
of its life and several times during the first year (Figure 49). 
Figure 49. — Molted Exo¬ 
skeleton of Lobster. 
One can tell just what kind 
of an animal this is simply by 
studying this cast-off shell. 
LABORATORY STUDY 
Place several crayfish in jars or aquaria and observe their behavior. 
Fill out the following report: 
Do THEY 
Move the 
Antennae ? 
DO THEY 
Walk 
Forward ? 
Do THEY 
Walk 
Backward 
Do they Use 
? Caudal Fin ? 
Do THEY 
Move Eyes? 
What Organs 
Make a Cur¬ 
rent in 
Water? 
