102 ANIMAL ACTIVITIES, 
Place some colored liquid from a pipette just in front 
of the thorax at the opening of the gill-cavity. 
For individual work by the pupil, the use of the 
shrimp is suggested because of the small expense and 
because of the necessary comparisons with the crayfish. 
Compare also with a lobster. The questions may be 
used with crayfish, shrimp, or lobster. 
Place the shrimp, crayfish, or lobster in a saucer 
with the head turned from you. 
Fic. 88.—Dorsal View of Crayfish. 
In what ways does the shrimp resemble the grass- 
hopper ? 
How does it differ ? 
In what respects does it resemble a spider ? 
How does the exo-skeleton compare with that of the 
insects ? 
How many segments do you find in the abdomen ? 
Can you find any indications of a division between 
head and thorax ? 
