by a transverse hinge and bears the anus. Carefully examine the 

 third abdominal somite. The following surfaces are found upon it : 

 (a) T erg um } the dorsal arched portion overlapped anteriorly by the 

 preceding tergum. (b) Sternum, the ventral portion between the 

 appendages, composed of a transverse bar and a more calcined 

 cuticle where movements take place in bending the abdomen, (c) 

 Pleuron, the downward projecting portion on each side, overlapped 

 in front by the pleuron of the preceeding segment. The appendages 

 are attached to the body by soft flexible cuticular parts of the exo- 

 skeleton. 



Each abdominal appendage consists of the following parts : 



a. Protopodite : This is the proximal part of the appendage and 

 is divided into a long joint, and a small ring-like piece by which it 

 is attached. It bears distally two parts. 



b. Endopodite : This is the part nearer the middle line. 



c. E.ropoditc: The portion farther from the middle line. 



C. CEPHALOTHORAX. 



a. The large shield-like part of the exoskeleton covering the 

 cephalothorax above and on the sides is the carapace, which is pro- 

 longed in front into the frontal spine or rostrum. 



b. A groove, the cerrical saturc runs across the carapace and 

 marks off the head from the thorax. 



c. On the ventral side the region between the appendages is very 

 narrow; the anterior appendages project forward and not downward 

 as do the more posterior ones. 



d. The locomotor appendages are attached to the thorax; the 

 posterior pair are upon a movable somite while all the others arise 

 from a fused single mass continuous with the head. 



e. The free lateral part of the carapace, above the appendages, 

 is the branchiostegite. Raise its edge and see that it covers the 

 gills. 



f . Respiratory organs : Remove one of the branchiostegites, 

 study the gills under water and observe : Six of them are attached 

 to the appendages, prodobrauchiae ; eleven of them are attached to 

 the soft cuticle joining the appendages to 'the body arthrobraiichiae. 

 At the anterior end of the branchial cavity a canal leads forward 

 toward the mouth and in this lies the flat part of the second maxilla 

 called the scaphognathite. 



D. APPENDAGES. 



Carefully remove all of the appendages from one side with all 



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