A CRAYFISH OR A LOBSTER 27 



Exercise 6. (b) If the animal be a female, remove and draw the 

 right-hand first swimmeret. 



Exercise 7. The walking legs (including the chelipeds) are called 

 periopods. 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 proximal seg- 

 ments (i.e., those nearest the body) constitute the protopodite 

 and the five distal ones (i.e., those farthest from the body) 

 the endopodite. The exopodite is not present. 



Exercise 8. The cheliped is composed of the same joints 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 (i.e., the posterior) 

 maxilliped and draw it on a large scale, disregarding the 

 gill which may be attached to it, and carefully label its 

 parts. Which terminal branch is the exopodite? 



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, the exopodite a much longer 

 structure next to it. A large epipodite is present. Label 

 all of these. 



