46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



THE PLEOPODS 

 THE MALE 



In the male blue crab, appendages occur only on the first two seg- 

 ments of the abdomen. The distal abdominal segments are much nar- 

 rower than in the female, and the third, fourth, and fifth segments 

 are fused so that their original sutures are scarcely visible, as I have 

 pointed out earlier in this study. 



In the first pleopod of the male the coxopodite is large and partially 

 sclerotized. The basipodite is irregularly shaped, and its distal border 

 is a membrane that attaches the long, whiplike flagellum and gives it 

 the necessary freedom of movement. In this membrane is likewise a 

 pocket in which the flagellum of the second pleopod normally rests. 



The name " flagellum " is chosen arbitrarily for the distal part of 

 the pleopod, as it does not show the character of a true flagellum. But 

 neither is there sufficient evidence for considering it a highly modified 

 endopodite or exopodite. 



The second pleopod is very much weaker than the first, which com- 

 pletely covers it. Its coxopodite is very thin-walled and partly mem- 

 branous. A small basipodite is present, controlled by a single muscle 

 originating in the coxopodite. The basipodite and flagellum are sclero- 

 tized, but an extensive membrane lies between them, as in the first 

 pleopod. Preaxially, the basipodite is represented only by a mem- 

 brane, as its sclerotized part is entirely postaxial in position. 



166. Musculus promotor coxopoditis I pedis spurii (fig. 14 A). — 

 This muscle originates on the ventral surface of the last thoracic 

 somite just lateral to the origin of the first ventral superficial abdomi- 

 nal muscle. It is inserted on the inner preaxial proximal border of the 

 coxopodite, which it erects strongly. This is the only extrinsic muscle 

 belonging to the first pleopod. 



167. Musculus abductor bosipoditis I pedis spurii (fig. 14 A). — 

 Arising on the walls of the outer part of the coxopodite, this muscle 

 is inserted on the outer proximal margin of the basipodite, which is 

 pulled away from the center by its contraction. 



168. Musculus adductor basipoditis I pedis spurii (fig. 14 A). — 

 This is a heavy muscle arising on the inner proximal walls of the 

 coxopodite. It is inserted on the inner proximal border of the basipo- 

 dite, which is pulled toward the center by its action. 



i6p. Musculus abductor Hagelli I pedis spurii (fig. 14 A). — This 

 small and compact muscle arises on the distal postaxial border of the 

 basipodite, and is attached to the extended proximal edge of the flagel- 

 lum. It causes the tip of the flagellum to move strongly outward. 



