A CRAYFISH OR A LOBSTER 33 
Bzercise 6. (b) If the animal be a female, remove and draw the 
right-hand first swimmeret. 
Exercise 7. The five pairs of walking legs (including the cheli- 
peds) are called periopods and belong to the thorax. Remove 
and draw the right-hand fourth periopod, disregarding the 
gill attached to it, and label the parts. It consists of seven 
segments, of which the two segments nearest the body con- 
stitute the protopodite, and the five farthest from the body 
the endopodite. The exopodite is not present. 
Exercise 8. The cheliped is composed of the same segments as 
the other periopods. With a strong knife split the claw 
lengthwise into two equal halves. Examine the muscles 
controlling the movable limb of the claw. There is a 
strong adductor muscle which closes it, and a weaker extensor 
muscle which opens it. Make a diagrammatic drawing 
illustrating them. 
Exercise 9. The three pairs of appendages directly in front of 
the chelipeds are the maxillipeds; they are thoracic append- 
ages which assist in the process of eating. Remove with 
forceps and scissors the right-hand third (é.e., the posterior) 
maxilliped; draw it on a large scale, disregarding the 
gill which may be attached to it, and carefully label the 
protopodite, exopodite, and endopodite. 
Exercise 10. Remove with the forceps the right-hand second 
maxilliped and draw it on a large scale. 
Exercise 11. Remove and draw the right-hand first maxilliped. 
The two large basal segments are the two segments of the 
leaf-like protopodite, the endopodite is a very small struc- 
ture next to the protopodite, and the exopodite is a much 
longer structure next to the endopodite. A large epipodite 
is present. Label all of these. 
