XIL] THE FRESH-WATER CRAYFISH. 141 



[S. The openings of the auditory organs. 

 . The openings of the green glands. 



These will be more readily found when the ap- 

 pendages on which they are situated have been 

 separated. See 21. f and gJ\ 



2. Examine carefully the third abdominal segment or 

 somite and its appendages. 



a. The segment proper : arched above ; flattened 

 below. 



a. Its dorsal part (tergum), with an anterior 

 smooth portion overlapped by the preceding 

 segment in extension of the abdomen, and a 

 posterior rougher part overlapping part of the 

 succeeding segment. 



ft. The ventral surface of the segment : united 

 with the corresponding portions of the preced- 

 ing and succeeding segments by a flexible 

 membrane. 



y. The point" of union of the appendages with 

 the somite. 



8. The sternum: that portion of the ventral sur- 

 face of the somite which lies between the 

 points of attachment of the appendages. 



e. The epimeron: the portion of the ventral sur- 

 face which lies on each side external to the 

 attachment of the appendage. 

 This region is very short and passes almost 

 directly into the inner walls of the pleuron. 



. The downward extension (pleuron) of the 

 lateral walls of the somite formed by the pro- 

 longation of the tergum and epimeron: the 



