XII. J THE. FRESH- WATER CRAYFISH. 135 



b. The great number of jointed limbs (appendages) 

 attached to the ventral aspect of the body : their 

 varying characters in different regions. 



c. The external apertures of the body. 



a. The mouth; seen by separating the append- 

 ages beneath the head. 



/3. The anus; a longitudinal slit beneath the telson. 



7. The paired genital openings: in the male, on 

 the first joints of the last pair of appendages 

 of the thorax : in the female, on the first joints 

 of the last thoracic appendages but two. 



[8. The openings of the auditory organs. 

 , , f c. The openings of tfw green glands. 



These will be more readily found when the ap- 

 pendages on which they are situated have been 

 separated. See 21. f and <?.] 



2. Examine carefully the third abdominal segment or 

 somite and its appendages. 



a. The segment proper: arched above; flattened 

 below. 



ct. Its dorsal part (tergum), with an anterior smooth 

 portion overlapped by the preceding segment 

 k in extension of the abdomen, and a posterior 

 rougher part overlapping part of the succeed- 

 ing segment. 



ft. The ventral surface of the segment : united 

 with the corresponding portions of the preced- 

 ing and succeeding segments by a flexible 

 membrane. 



