80 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



with the evolution of this versatile accessory 

 feeding mechanism. The meropodite product or 

 muscle originates on the medial side of the ischi- 

 opodite, near the exopodite adductor, and inserts 

 on a small apodeme on the dorsal surface of the 

 meropodite. The muscle lifts the meropodite and 

 other distal elements towards the ventral surface 

 of the mandibles. The same muscle appears in 

 Pandalus, Astacus, and Callinectes. 



MEROPODITE REDUCTOR MUSCLES OF SECOND 

 MAXILLIPED 



Figure 45 



Penaeus has two meropodite reductor muscles. 

 The medial reductor originates on the medial wall 

 of the ischiopodite, ventrad of the meropodite 

 productor, and inserts on an apodeme on the ven- 

 tral margin of the meropodite. Another reductor 

 muscle originates on the anterodorsal surface of 

 the ischiopodite and passes to the same apodeme 

 as the medial reductor. The muscles turn the 

 meropodite ventrad. The meropodite reductors 

 of Penaeus have partial counterparts in the sec- 

 ond maxilliped of Astacus, Pandalus, and Callin- 

 ectes, but in the latter only one reductor has been 

 described. 



CARPOPODITE ABDUCTOR MUSCLES 

 OF SECOND MAXILLIPED 



Figure 45 



Two carpopodite abductor muscles are found in 

 the second maxilliped of Penaeus. The smaller 

 of these originates on the dorsal side of the merop- 

 odite and inserts on the common abductor 

 apodeme on the lateral edge of the carpopodite. 

 The larger abductor takes origin on the lateral 

 side of the meropodite, proximally. The muscle 

 runs out along the lateral side of the meropodite 

 and attaches to the abductor apodeme on the 

 carpopodite. The two muscles turn the small 

 carpopodite laterad. However, with respect to 

 the gnathal surface of the dactylopodite, the 

 carpopodite abductors cause functional adduc- 

 tion, in consequence of the hooked shape of the 

 endopodite. The large carpopodite abductor 

 muscle is the same muscle as the carpopodite ab- 

 ductor in Astacus, Pandalus, and Callinectes, 

 The small abductor in Penaeus is not described in 

 any of the foregoing crustaceans. 



CARPOPODITE ADDUCTOR MUSCLE 

 OF SECOND MAXILLIPED 



Figure 45 



The carpopodite adductor muscle runs from the 

 proximal end of the meropodite to an adductor 

 apodeme on the medial side of the carpopodite. 

 The muscle is less powerful than the carpopodite 

 abductors. The adductor turns the carpopodite 

 mesad, but as a result of the distal hook, the 

 gnathal surface of the dactylopodite is moved 

 laterad. The carpopodite adductor of Penaeus is 

 fully homologous with the carpopodite adductor 

 in the other crustaceans to which reference 

 has been made. 



PROPODITE PRODUCTOR MUSCLE 

 OF SECOND MAXILLIPED 



Figure 45 



The propodite productor muscle is a short, 

 thick structure originating on a proximal, ven- 

 tral part of the carpopodite, and running to a 

 broad apodeme on the ventrolateral side of the 

 propodite. Its contractions turn the propodite 

 and dactylopodite ventrad. The propodite pro- 

 ductors in Penaeus are homologous with the 

 propodite productor in Astacus, Pandalus, and 

 ( iillinectes. 



PROPODITE REDUCTOR MUSCLE OF SECOND 

 MAXILLIPED 



Figure 45 



The propodite reductor muscle occupies the 

 dorsal part of the carpopodite in the shape of a 

 fan. The broad portion originates in the proximal 

 region of the carpopodite. The muscle becomes 

 narrow as it inserts on a little apodeme on the 

 dorsal side of the propodite. The muscle turns 

 the propodite and dactylopodite dorsad, about the 

 horizontal axis through the condyles. The propo- 

 dite reductor muscle of Penaeus is represented in 

 the second maxilliped of the three crustaceans to 

 which frequent reference has been made. 



DACTYLOPODITE PRODUCTOR MUSCLE OF 

 SECOND MAXILLIPED 



Figure 45 



The dactylopodite productor muscle is a small, 

 fan-shaped muscle that originates proximally in 

 the propodite and inserts on the ventral margin of 

 the dactylopodite. It serves to straighten the 



