E. A. Andreios — Anatomy of the Spider Crab. 103 



tlie walls of the lower apodeiiial cell of its own segment and con- 

 nected with the anterior edge of the joint by a chitinoiis, tendon-like 

 process of that edge. 



Backward movement is produced by muscles attached to the walls 

 of the upper cell of the segment and similarly connected with the 

 posterior edge of the joint. The articulations between the joints, 

 except between the second and third, are similar pivot and socket 

 arrangements, set at right angles to the plane of movement, which 

 is alternately vertical and horizontal. With the exception of the 

 third joint, each is moved by two sets of muscles connected with 

 opposite edges of the proximal end by two tendons, and arising from 

 the walls of the preceding segment, but the first joint being short 

 the muscles of the second extend into the lower apodemal cell and 

 are thex*e attached. The articulation between the second and third 

 joints is peculiar ; they are united obliquely by a very firm mem- 

 brane, which allows of a slight twisting or rotary motion of the 

 third upon the second. The muscles arising from the walls of the 

 second joint are connected by two short tendons with the posterior 

 edge of the third joint. 



The first pair of legs (fig. '7), which are not so truly locomotive in 

 function as the others, differ in having the fifth joint enlarged, flat- 

 tened, with the tip prolonged so as to form with the modified termi- 

 nal joint a chela or claw, and in bearing a sjjine (t) on the proximal part 

 of the third joint. 



In the other legs (fig. 6) the terminal joint is conical and dark 

 amber-colored at the tip. These chelate appendages differ, also, in 

 the two sexes. 



In the female (fig. V) they are short, scarcely longer than the fifth 

 or shortest pair of legs. In the male these chelate legs become 

 nearly or quite as long as the second pair of legs and much stouter 

 than in the female. The third and fifth joints are also longer in pro- 

 portion to the length of the leg in the male than in the female, and 

 the sockets at the proximal end of the fifth joint are not so promi- 

 nent. These appendages present only slight and inconstant differ- 

 ences on the two sides of the body. 



The manducatory appendages, which prepare the food and pass it 

 to the mouth, are contained in the peristomial depression, and in- 

 clude one pair of mandibles and five pairs of flattened organs directed 

 forward and overlapping one another. The densely calcified mandi- 

 bles stand on either side of the mouth, at the center of the peristome, 

 and bear two-jointed palpi on their anterior faces. The right mandi- 



