HARD PARTS OF THE CRAYFISH OR LOBSTER. 187 



7^. The narrow sterna of the abdominal segments, be- 

 tween the bases of the swimming feet. 



i. The anus, in the soft integument of the lower sur- 

 face of the telson. 



k. Note that the sternal surface which carries the eyes, 

 antennules, and antennae, makes a sharp angle the cra- 

 nial flexure with the sterna of the remaining segments. 



I. Make a sketch showing these points. 



III. Removing the third abdominal segment, with its ap- 

 pendages, notice : 



a. The arched dorsal surface of the segment, the 

 tergum. 



b. The flaps, or lateral walls, pleura of the tergum. 

 The posterior margin of each pleuron overlaps the smooth, 

 anterior margin of the succeeding pleuron. 



c. The narrow sternum, forming that portion of the 

 ventral surface which lies between the appendages. 



d. The flexible membrane which covers the space be- 

 tv/een the sterna of adjacent segments. 



e. The point of union of the appendage with the seg- 

 ment. 



f. The '/;////' m, or those portions of the ventral surface 

 which lie external to the points of attachment of the ap- 

 pendages. The epimera are very short, and pass almost 

 directly into the inner walls of the pleura. 



g. The appendages or pleopods of the third abdominal 

 segment consist of : 



1. A short, two-jointed, basal portion, or protopodite, 

 consisting of a shorter proximal, and a longer distal piece. 



2. Two flattened plates, an outer exopodite, and an inner 

 endojiodife, attached to the distal end of the protopodite. 



h. Make a sketch of the segment, showing all these 

 points. 



