132 THE CRAYFISH 



i. The two joints of the protopodite are expanded 

 on the inner side, forming a large two-lobed 

 lamella. A broad plate, the epipodite, takes 

 the place of a gill. 



ii. The endopodite is very small and two-jointed. 



iii. The exopodite resembles that of VII. 



3. The head appendages consist of three pairs of oral 

 appendages or jaws, V. to III., placed at the sides of 

 the mouth ; and two pairs of pre-oral appendages, 

 II. to I,, at the front of the head. 



V. The second maxilla consists of a protopodite, an 

 endopodite, and on the outer side an organ sub- 

 servient to respiration, the scaphognathite. 



i. The protopodite consists of two joints, coxopodite 

 and basipodite, each of which is expanded on 

 its inner side into a bilobed lamella. 



ii. The endopodite is small, pointed, and unjointed. 



iii. The scaphognathite is an elongated plate at- 

 tached by the middle of its inner edge to the 

 outer side of the protopodite. It may be 

 regarded as the exopodite and epipodite fused 

 together. It serves to keep a current of water 

 flowing through the gill-chamber (p. 136). 



IV. The first maxilla is small. The two joints of the 

 protopodite extend inwards as thin curved lamellae, 

 and the endopodite is a small plate to their outer 

 side. There is no exopodite. 



III. The mandible consists of a very stout undivided 

 protopodite, forming the powerful jaw at the side 

 of the mouth ; and an endopodite, which forms a 

 small three -jointed palp, lying in a groove on the 

 front of the protopodite. 



Before removing the mandible, note the position of the two 

 2iivots about which it turns, and the points of insertion of the 

 tendons of its abductor and adductor muscles. 



Immediately in front of the first maxilla and 



