246 MANUAL OF ELEMENTARY ZOOLOGY 



structure directed forwards. The exopodite is a wide plate 

 projecting backwards and forwards from the outer side of 

 the limb and known as the scaphognathite. The second 

 maxilla lies under the front end of the branchiostegite, and 

 the function of the scaphognathite is to set up a current of 

 water over the gills by baling it forwards out of the gill 

 chamber. The sixth limb, or first maxilliped, is the first 

 of those which belong to the thorax. Two broad lobes 

 represent its coxopodite and basipodite, the endopodite is 

 small and two-jointed, and the exopodite, shaped like that 

 of the third maxilliped, is large. The epipodite is present 

 as a very large plate, which does not bear a gill. The 

 second maxilliped 'is much like the third, but has a smaller en- 



cp. 



Fig. 157. — The first walking leg of a crayfish. Letters as in Fig. 156. 



dopodite and a relatively larger exopodite. The third maxil- 

 liped has already been described. Behind the maxillipeds 

 come five pairs of legs or pereiopoda, of which the first, the 

 ninth of the whole series of limbs, bear great pincers and are 

 called the chelipeds, the rest being the walking legs. In each 

 of these limbs the exopodite is wanting and the endopodite is 

 long and strong and consists of five joints, named as in the 

 third maxilliped. In the chelipeds and the walking legs 

 of the first two pairs the last joint but one has a projection, 

 against which the last joint bites so as to form a pair of 

 pincers. An epipodite bearing a gill is present upon each 

 of the legs except the last pair. On the coxopodite of the 

 second walking leg of the female is a round opening, 

 through which the eggs are laid, and the sperm of the male 



