Xri.] THE FEESH-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. 



^8. The amis; 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. 



[S. The openings of the OMclitory organs.'j^.tx. §-' -~-y 

 c The openings of Hie green glands. /■^- 9 i '■''' ' - 

 These will be more readily found when the ap- 

 pendages on which they are situated have been 

 separated. See 21. /and j.] 



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 succeed- 

 ing segment. 



/3. The ventral surface of the segment: united 

 with the corresponding portions of the preced- 

 ing and succeeding segments by a flexible 

 membrane. 



