12 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



CYCLOSALPA PINNA TA, solitary form.i 



Plate 1, figs. 1 and 2; plate 2, fig. 6. 



Referring to figure 1, which shows the solitary form of Cyclosalpa 

 pinnata as seen from the right side, observe the general shape of the 

 body, keg-shaped, with the anterior end rather abruptly narrowed 

 and the posterior end more tapering. The test is delicate and thin, 

 being thickest ventrally. The luminous organs are seen halfway up 

 each side of the body, as a series of five spindle-shaped glands between 

 the body muscles. In structure they resemble blood lacunae full of 

 blood corpuscles, and such may have been their derivation, though 

 now their cells are modified, each containing numerous yellow gran- 

 ules of a substance which by oxidation produces light. The luminous 

 organs of Pyrosoma are very similar histologically. 



The ribbon-shaped muscles are shown in figure 1. For convenience 

 of description these may be divided, chiefly according to function, 

 into body muscles (indicated by Roman numerals), oral muscles, and 

 atrial muscles. There is also another muscle which in the more 

 primitive Salpidae is associated with the body muscles but in the 

 more modified species is more connected with the oral muschs. 

 This is usually called by German zoologists the "Bogenmuskel." 

 We will refer to it as the intermediate muscle (i. m. in the figures). 



Of the body muscles there are seven, as numbered in the figure. 

 They are arranged like the hoops of a keg, but each is interrupted on 

 the mid line both dorsally and ventrally. The intermediate muscle is 

 continuous ventrally with its fellow of tho othor side, as are the lip 

 muscles. It probably shares with tho oral muscles the function of 

 strengthening the lower lip which acts as a valve to close the mouth 

 when the water is expelled throught the atrial aperture by tho con- 

 traction of the body muscles (fig. 6). 



Most prominont of the oral muscles are the horizontal oral retractors, 

 one on each side, running forward from the first body muscle to the 

 angle of the mouth (fig. 1). Anteriorly each divides into two mus- 

 cles, oral sphincters, which run around the lower lip, one near the edge 

 (1. 1 ), the second a little farther back (1. 2). The anterior two sphinc- 

 ter muscles of the. upper lip (u. 1 and u. 2) are almost but not quite 

 united to the retractor at their ventral ends. In addition to the oral 

 retractor j ust described and the sphincters united to or acting in con- 

 j unction with it, there is on each side a more ventral oral retractor, 

 running from lower down on the first body muscle diagonally forward 

 and upward, passing outside of the intermediate muscle, to a point 



i The drawings and descriptions are based on studies of abundant material of both solitary and aggre- 

 gated forms of this species, chiefly from tho central Mediterranean Sea and otf the Atlantic coast of North 

 America. Compare United States National Museum Collections, Cat. No. 6460. 



