366 THE CRAYFISH CHAP. 



'arranged in a single series, strongly calcined, and with the 

 exception of the second and third, which are fused move- 

 ably articulated with one another. The second podomere, 

 counting from the proximal end, bears a many-jointed 

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

 plate (ep) having a plume-like gill (g) attached to it. The 

 first two segments of the axis form the protopodite (pr. i, 2), 

 its remaining five segments the endopodite (en. i, 5), the 

 base of which is toothed ; and the feeler, which is directed 

 outwards, or away from the median plane, the exopodite 

 (ex). 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. 



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

 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 chela : 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 important weapon of offence 

 and defence. The second maxilliped 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 epipodite. 



The head bears a pair of mandibles and two pairs of 

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

 aperture a pair of antennules and of antenna. The hind- 

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

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



