102 £^. A. Aitdreios — Anatomy of the Spider Crab. 



jointed, well calcitied organs, arising from the first and second seg- 

 ments. The basal joint of the first pair (/y, fig. 4) is large, trian- 

 gular, immovably united to the sternum, and projects backward so that 

 the following joint appears to arise from the second segment. The 

 third joint {d) is a long, styliform organ, curving outward and 

 bearing a small, membranous, triangular process (/j>) near the tip. 

 The second joint (c) is small, and serves to make flexible connec- 

 tions between the first and third. 



The second pair of appendages are much smaller than the first, 

 and Avhen at rest lie in cavities on the posterior face of the latter, at 

 the base of the third joint. They have, like the first pair, an immova- 

 ble basal joint (6', fig. 4) followed by a small second joint ; but the 

 third joint {d') is short, straight, and terminates in a membranous 

 papilla (/>'). 



In the female there are four pairs of abdominal apijeudages (fig. 3) 

 borne near the outer edges of the broad sterna of the second, third, 

 fourth, and fifth abdominal segments. Each consists of two long 

 slender branches [ex, en, fig. 5), articulated to the abdomen by a par- 

 tially calcitied membrane (jyr) representing a basal joint. The outer 

 branch, exopodite (ex), curves inwards and is densely covered with 

 soft setffi on its outer face. The inner branch is composed of a shorter 

 proximal and a longer distal portion freely articulated to the i)roxi- 

 mal. The distal portion stands nearly at right angles with the 

 proximal, which is directed toward the medial line, and is divided 

 into about fifteen imperfect joints by grooves on the upper or pos- 

 terior face. A few similar grooves exist on the proximal portion ; 

 from the edges of all, lung setae arise. These appendages, like those 

 of the male, are ordinarily turned backward against the sternal sur- 

 face (fig. 3), and are concealed by the abdomen. They difterbut lit- 

 tle on the different segments, the length becoming less and the 

 breadth of the outer branch greater tOAvard the end of the abdo- 

 men. They are used for carrying the eggs. 



The locomotive organs are five pairs of long, cylindrical, slendei-, 

 six-jointed legs, attached between the edge of the carapace and that 

 of the sternal plastron. 



The anmdar basal joint (e, figs. 6, 7) moves horizontally on two 

 pivot-like processes fitting into small cavities or sockets, a pivot on 

 the lower edge [x) playing in a socket in the plastron, and a socket in 

 the upper edge (s) receiving a pivot from the pleural wall, except on 

 the fifth pair, where the upper socket is replaced by a pivot. Each 

 of these joints is moved forward by powerful muscles attached to 



