ARTHROPODA. 



263 



Make a sketch of an imaginary cross-section showing the 

 relation of these parts to each other, together with the 

 attachment of the appendages. 



IV. Appendages. Group them into regions and notice the 

 general differences and the differences in the uses to 

 which they are put. If time will allow, study the ap- 

 pendages in detail as follows : 



1. Begin with the third or fourth abdominal appendage (swimmerets) 

 making the drawings necessary to show the parts : 



Protopodite, or basal portion. 



Exopodite, or external branch. 



Endopodite or internal (median) branch. 



Compare all the abdominal segments with that studied. Do different 

 individuals agree in the appearance of the first and second abdominal 

 segments? Compare the last segment (telson) with those studied. How 

 many segments in the abdomen? Of what parts is the tail fin made up? 



2. Cephalo -thoracic Appendages. Remove with scissors the over- 

 arching portion of the carapace and expose the base of the appendages. 

 Find the third maxilliped (the first appendage in front of the large claw). 

 Remove by inserting a scalpel and bringing away all that belongs to it. 



Identify : 



Protopodite, of two segments (coxopodite, next the body, and 



basipodite). 



Endopodite and exopodite. How many pieces in each? 

 Epipodite, lying in the gill-chamber. Are there any special out- 

 growths on it ? 



Study and compare with this the large claw, and the other walking 

 appendages. Which part is wanting in these, exopodite or endo- 

 podite? Reasons for your view? How do these five appendages 

 differ frpm each other. 



Examine and compare the appendages in front of the third maxilliped 

 in order : 



Second maxilliped. 



First maxilliped. 



Second maxilla. 1 



First maxilla. 



Mandible. f Head P arts " 



Antenna. 



Antennule. 



What are the evidences that the antennae and antennules are homolo- 

 gous with those already described? 

 Revise your estimate of the number of segments. 



