62 
CRUSTACEANS AND RELATED FORMS 
Laboratory study on the appendages. Examine more fully than in 
the above and report the work of each pair of appendages. Compare 
one of the abdominal appendages with those used in walking and feel¬ 
ing. What is the work of the large pincers? How many fin-like 
appendages are found in the mouth region? Notice that one of the 
mouth appendages has a flat part that extends in front of the gills. 
This part of the appendage is called the gill scoop or bailer. Describe 
how the appendages show at least three useful adaptations in the life 
of the crayfish. 
44. Food and Food-getting. — The food of the crayfish is 
both plant and animal, living and dead. One of the simple 
water plants, Chara (ka/ra), furnishes the crayfish with 
Figure 50. — Organs of Crayfish. 
Note that the gills are outside of the body. In the posterior part of the 
abdomen, the muscles have been removed to show the nerve ganglia 
which extend the entire length of the body. 
lime for its skeletons. Shells of snails and their own shed 
skins also help to supply lime. Crayfish seize food with 
their pincers and move it towards the mouth. Small food 
particles are also carried towards the mouth by currents of 
water produced by the mouth parts and the abdominal 
appendages. Particles of food are torn loose by the teeth 
or mandibles. 
