K. Stephensen: The Copulatory Organ (Petasma) of Sergestes vigilax (Stimpson) H. J. H. 5 



My fig. 3 corresponds with the stage figured by Pesta (Zool. Anzeiger, voJ. 42, 

 No. 9, 29. Aug. 1913, p. 406, fig. 5). The appendage turned towards the pleopode is 

 in the distal part of its edge of fixation provided with a little bud, later on (figs. 

 5 — 6) becoming a large process with a hook in the end. The proximal end of the 

 petasma has a pair of lappets (figs. 5 — 6), and the appendage next to the middle- 

 line has been folded (figs. 4 — 6), at the same time as the edge joining the corres- 

 ponding part of the petasma in the other pleopode has been provided with small 

 hooks, joining with those in the petasma of the other side, quite as in the maxilli- 

 pedes of the Isopoda. The 4 buds in the apex of the petasma have grown longer; 

 a pair of them or at least one (fig. 6) is provided with cleft spines. In one of the 

 specimens (fig. 4) the petasma ends with 5 appendages, with a little one besides the 

 4 already mentioned. 



Senna's figs. (1. c. p. 292 — 93, figs. 4 — 5) correspond with my fig. 4, but he gives 

 no description, only referring to his figures. 



As may be seen the petasma varies very much with the age, and thus may 

 not be used as a specific-character. The petasma does not seem to have roused the 

 interest of carcinologists very much. The best description and figure, as far as I 

 am aware, are given by S. J. Smith in the "Blake"-Decapoda (Bull. Mus. Comp. Zool., 

 Harvard College, vol. 10, No. 1, 1882, p. 99 {Sergestes rohustus), PI. 16 fig. 8); although 

 he has described the organ in another species, the whole corresponds very well with 

 my fig. 6. 



