186 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



these are substantially alike, and consist of an anterior, 

 smooth, highly-polished portion, which is overlapped by 

 the posterior margin of the preceding segment, and a 

 rougher, posterior portion, the posterior margin of which 

 projects over the anterior margin of the succeeding seg- 

 ment. 



2. The seventh, or terminal joint of the abdomen, the 

 telson, is a flattened, somewhat triangular plate. 



3. At the sides of the telson are the paddle-shaped 

 swimmerets^ the appendages of the sixth abdominal seg- 

 ment. 



g. Make a sketch of the dorsal surface, showing all 

 these points. 



II. The ventral surface. 



a. Notice the lateral edges of the carapace, the rostrum, 

 eyes, antennules, and antennae, as before. 



h. Back of these, the complicated mouth parts, meeting 

 each other on the median line. 



c. Push these apart, and notice between them the aper- 

 ture of the mouth. 



d. Back of the mouth parts are the five pairs of walk- 

 ing legs. 



e. BetAveen the basal joints of each pair is a plate, the 

 sternum, or ventral portion of the segment, to which the 

 pair of limbs is attached. The sterna Avhich correspond 

 to the first four pairs of limbs are immovably united to 

 each other, while the fifth is slightly movable. 



f. Along the outer edges of the ventral faces of the 

 abdominal segments are the thin, flat, swinnning feet, 

 varying somewhat in number and form, according to 

 the sex. 



g. The swimming feet of the sixth abdominal segment 

 are much larger than the others, and are the swimmerets 

 which are visible in a dorsal view. 



