A CRAYFISH OR A LOBSTER 25 



and is sometimes called a uropod, but yet has the typical parts. 

 Label its parts. 



Exercise 6, a. If the animal is a male, remove and draw the right- 

 hand first and second swimmerets. These are modified from the 

 typical structure to serve as copulatory organs. 



Exercise 6, &. If the animal is a female, remove and draw the right- 

 hand first swimmeret. 



Exercise 7. The five pairs of walking legs (including the chelipeds) 

 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 

 proximal segments, those nearest the body, constitute the protopo- 

 dite, and the five distal ones, those 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 diagram- 

 matic drawing illustrating them. 



Exercise 9. The three pairs of appendages directly in front of the 

 chelipeds are the maxillipeds ; they are thoracic appendages which 

 assist in the process of eating. Remove with forceps and scissors 

 the right-hand third (that is, 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 maxil- 

 liped 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 leaflike 

 protopodite, the endopodite is a very small structure 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. 



Exercise 12. The two pairs of delicate appendages in front of the 

 maxillipeds are the maxillae ; they are cephalic appendages. Re- 

 move with forceps the right-hand second maxilla and draw a large 

 outline of it. The protopodite is wide and leaf like ; the endopodite 

 is small ; the exopodite is wide and with the epipodite forms a broad 

 plate, called the scaphognathite, which is used by the animal to 

 maintain a current of water from the gill chamber. 



