CALLINECTES HASTATUS. 135 



External Anatomy. — 1. The body is composed of cephalo- 

 thorax and abdomen. Dorsally note the shape of the carapace 

 and the position of the abdomen. The size of the abdomen 

 differs in male and female. Why should it be larger in the 

 female ? 



2. Note the antcnnce, antennules, and eyes, and see how they 

 are packed away in recesses in the carapace. In the living 

 animal see if any of these are frequently moved. 



3. The third maxillipeds are flattened and cover the other 

 mouth appendages. 



4. Straighten the abdomen and note the anus. Compare the 

 aljdomen of a male with that of a female and both with that of the 

 lobster. The dorsal side of each segment is covered by a tergum. 

 The covering between each pair of pleopods is the sternum, the 

 immovable flap lateral to them is the pleuron. Compare the ab- 

 dominal appendages or pleopods of a male and a female. 



5. The ventral side of the cephalo-thorax is covered by the 

 sternal plastron. Note the eight sterna and six pairs of lateral 

 episterna. 



6. In the female find the openings of the oviducts in the fifth 

 sternum. 



Meike a drawing of the ventral side. 



7. Expose the gill chamber and compare the gill distribution 

 with that of the lobster. 



8. Remove the left third maxilliped entire, and compare it 

 with the same appendage of a lobster. The protopod is com- 

 posed of two segments {coxopod and hasipod). The endopod 

 has five pieces {ischipod, meropod, carpopod, propod, and dactyl- 

 opod). The exopod has two large and many small segments. 

 Attached to the coxopod laterally is an epipod which extended 

 into the gill chaml^er. 



9. Remove the remaining mouth appendages on the left side 

 and compare them with the third maxilliped. They are: second 

 maxilliped bearing epipod and two small gills; first maxilliped 

 with an epipod; second maxilla with a flattened exopod, called 

 the scaphoghathite, which has a special function that should be 



