42 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



.—dorsal 

 seta 



A. Lateral View 



ventral 

 seta^ 



y ventral 

 pit 



B. Ventral View 



Figure 2i). — Enlargement of proximal segments «>f antennal flagellum showing sensory structures. 



(luctor muscle in rotating the. fourth segment on 

 the third segment. In opposition to the fourth 

 segment adductor, the fourth segment abductor 

 turns the fourth antennal segment laterad a short 

 distance. Xo homolog of this muscle is here 

 advanced. 



FOURTH ANTENNAL SEGMENT PROMOTOR 



MUSCLES 



Figure 24 



The fourth antennal segment promoter mus- 

 cles (fig. 24) are situated within the body of the 

 third antennal segment. At least three of these 

 muscles occur in Penaeus. The short, thick pro- 

 motors originate throughout the ventral surface 

 of the third antennal segment and insert at their 



narrow apical tips on an apodeme of the fourth 

 antennal segment. Contractions of the fourth an- 

 tennal segment promotors move the fourth seg- 

 ment and the distal antennal parts anteriorly. 

 How 7 these muscles are represented in the other 

 crustaceans referred to in this paper is uncertain. 



FIFTH ANTENNAL SEGMENT PROMOTOR 

 MUSCLES 



Figure 24 



The fifth antennal segment promoter muscles 

 (fig. 24) are comprised of a tuft of at least four 

 small muscles restricted to the. fourth antennal 

 segment. The muscles originate on the lateral 

 and posterior margin of the fourth article, and 

 attach to an apodeme arising from the posterior 



