A CRAYFISH OR A LOBSTER 33 



Exercise 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 (i.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. 



