CRAWFISH 73 



have been prepared. The thorax includes segments V to XII 

 and bears the three pairs of maxillipeds and five pairs of walking 

 legs. The abdomen comprises segments XIII to XVIII and the 

 telson. 



10. In the same manner as directed above study the third 

 maxilliped which lies immediately anterior to the cheliped. Ex- 

 amine carefully while still in place to make sure of proper ar- 

 rangement of parts, then remove and draw ventral view, X4 

 Distinguish protopodite (made up of coxopodite and basipodite), 

 exopodite, endopodite, epipodite, and gills. 



11. Remove, study, and draw second maxilliped. Continue 

 the study, using the first maxilliped. Draw. Do you find gills on 

 each of these? 



12. The second maxilla has a broad, thin protopodite near 

 the median line of the body. The exopodite is a tough mem- 

 branous structure, the gill bailer, which at its posterior extremity 

 is continuous with another membranous projection, the epipodite. 

 The endopodite is a very minute projection between protopodite 

 and exopodite. Draw. 



13. The first maxilla consists of only two conspicuous, flat- 

 tened lobes, the outer one of which is the endopodite and the 

 other the protopodite. 



14. All the hard part of the mandible and the basal joint of 

 the small feeler-like structure attached to its outer margin are 

 protopodite. The two remaining segments of the feeler-like ap- 

 pendage are endopodite. Draw. 



15. Examine the second pair of feelers, the antennae, and 

 compare the parts with those of the third abdominal appendage. 

 Draw left antenna X3- In this as well as in other parts of the 

 outline the position of an appendage is determined by the point 

 of its attachment to the body wall, not by the distance the appen- 

 dage extends beyond the body. 



16. Note the small white elevation on the ventral side of 

 the basal joint of each antenna. The small opening in each of 

 these elevations is the excretory opening. 



