138 THE CRAYFISH. 



XVIII. The fifth abdominal appendage is a small 



swimmeret. 

 i. The protopodite is two-jointed, the small proxi- 

 mal segment being named coxopodite, the 

 longer distal segment the basipodite. 

 ii. The endopodite is a many-jointed filament 

 covered with setse. Its first segment is the 

 largest. 

 iii. The exopodite is similar, but smaller. 



XVII. and XVI. These two pairs of appendages closely 

 resemble XVIII. 



XV. In the female this resembles XVIII., but is liable 

 to reduction, and may be absent. 



In the male it is normally turned forwards 

 and is specially modified for transferring the 

 spermatozoa to the female. The protopodite 

 and exopodite resemble those of XVIII., but the 

 large proximal segment of the endopodite is pro- 

 duced distally on its inner side into a short 

 plate, rolled longitudinally upon itself to form 

 an imperfect tube : the remainder of the endo- 

 podite is a small jointed rod as in XVIII. 



XIV. In the female this is reduced or absent. 



In the male it is modified for the same pur- 

 pose as XV. It is an unjointed rod, the distal 

 portion of which is flattened and rolled upon 

 itself to form an imperfect tube. It is probably 

 formed of the protopodite and endopodite fused 

 together. 



2. ^he thoracic appendages, of which there are eight pairs, 

 fall readily into two groups : a posterior group of 

 five pairs of large appendages, XIII. to IX., used for 

 walking and prehension, and devoid of exopodites ; 

 and an anterior group of three pairs of maxillipedes 

 or foot-jaws, VIII. to Vf., which possess both exo- 



