146 THE CRAYFISH. 



iii. The exopodite is similar, but larger, and divided 

 by a transverse binge into two parts. 



XVIII. The fifth abdominal appendage is a small swim- 

 meret. 



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 setae. 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 endopodite 

 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 purpose 

 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. The 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; 



