LESS. XXVII 



EXTERNAL CHARACTERS 



319 



verse depression, the cervical groove. The carapace is 

 developed from the dorsal and lateral regions of both head 

 and thorax : it is free at the sides of the thorax, where it 



FIG. 81. Side view of male Fresh-water Crayfish, natural size. 



The cephalothorax is covered by the carapace, produced in front into 

 a rostrum (r] and divisible into cephalic (cth) and thoracic (kd) portions 

 separated by an oblique cervical groove. The line from kd points to 

 the gill-cover. 



The abdomen (ab} is made up of six movably articulated segments 

 (xiv-xix), followed by a telson, the extremity of which is indicated by 

 the lower end of the bracket from ab. 



The eye-stalk is seen at the base of the rostrum. 



Of the cephalic appendages the antennule (a 1 ) and antenna (a 2 ) are 

 shown ; of the thoracic appendage the third maxilliped (8), the enlarged 

 first leg or cheliped (9), and the four slender walking legs (10-13) ; of 

 the abdominal appendages three pleopods and the uropod (18). 



(From Lang, after Huxley. ) 



forms a flap or gill-cover (Fig. 83, B, Brstg) on each side, 

 separated from the actual body-wall by a narrow space in 

 which the gills are contained. 



From the ventral surface spring a number of paired limbs 



