324 THE CRAYFISH i ess. 



feeler-like organ (ex), and from the first springs a thin, folded 

 plate (e/>) having a plume-like gill (g) attached to it. The 

 first two segments of the axis form the protopodite, its 

 remaining five segments the endopodite, and the feeler, 

 which is directed outwards, or away from the median plane, 

 the exopodite. The folded plate is called the epipodite : in 

 the natural position of the parts it is directed upwards, and 

 lies in the gill-cavity between the proper wall of the thorax 

 and the gill-cover (Fig. 87, \, pbd.). 



The five legs (8) differ from the third maxilliped in cheir 

 greater size, and in having no exopodite : in the fifth or last 

 the epipodite also is absent. The first three of them have 

 undergone a curious modification, by which their ends are 

 converted into pincers or chelce : the fourth segment of the 

 endopodite (sixth of the entire limb, en. 4) is produced dis- 

 tally so as to form a claw-like projection {en. 4'), against 

 which the terminal segment (en. 5) bites. The first leg is 

 much stouter than any of the others, and. its chela is of 

 immense size, and forms an imj)ortant weapon of offence 

 and defence. The second viaxillif'ed resembles the third, 

 but is considerably smaller : the first (6) has its endopodite 

 greatly reduced, the two segments of its protopodite large 

 and leaf-like, and no gill is connected with the ei)i{)odite. 



The head bears a pair of mandibles and two pairs of 

 maxill8e in relation with the mouth, and in front of that 

 aperture a pair of antennules and one of antennae. The 

 hindmost appendage of the head is the second maxilla (5), 

 a leaf-like appendage, its protopodite being cut up into 

 lobes, while the exopodite is modified into a boomerang- 

 shaped plate, which by its movements produces a current of 

 water over the gills. The first maxilla (4) is a very 

 small organ, having neither exo- nor epipodite. The ma7i- 

 dible (3) is a large, strongly calcified body, toothed along 



