So Papers from the Marine Biological Laboratory at Tortngas. 



line from its anterior end to the region of the digestive organs, but my older 

 and better preserved specimens show a sharp upward bend at the anterior 

 end (plate i, figure 5). 



THE MUSCLES OF THE AGGREGATED FORM OF SALPA FLORIDANA. 

 (Plate i, figs. 5 and 6; plate 2, fig. 9.) 



Figure 6 shows the muscles in ventral view ; figure 9 in dorsal view, and 

 figure 5 in side view. In describing the muscles I have used the method 

 of designating them which is most convenient for comparing them with 

 those of other species, and for studying their homologies. Apstein's account 

 and figures of these muscles is so unsatisfactory that I shall not attempt to 

 compare my own account with his. 



In the solitary 6". florid a no all the muscles except i, 2, 13, 14, and 15 

 are incomplete dorsally, and do not cross the dorsal middle line, while all 

 except ii are complete ventrally and cross the middle line. In the aggre- 

 gated form all the muscles cross the middle line of the dorsal surface, while 

 only 6, 7, 8, 9, and 10 cross the middle line of the ventral surface. The 

 muscles at the anterior end of the body, which I have numbered from i to 

 6, can be identified without difficulty with those of the solitary form, which 

 I have designated by the same numbers in figures i and 2. The muscles 

 back of 6 are highly specialized, and it is difficult to homologize them with 

 equivalents in the solitary form without comparative study of the other 

 species of Cyclosalpa. I find reason, which is given in Part III of this 

 memoir, on the subgenus Cyclosalpa, for a very exact homology between 

 the muscles, and the reader may refer to this discussion. 



The following are the most conspicuous and important differences be- 

 tween the muscles of the solitary form and those of the aggregated form : 

 In the aggregated form, muscle 3 is prolonged ventrally into that part of 

 the body-cavity which is included in the process that joins the aggregated 

 form to the other members of the community, and it there unites with mus- 

 cle 7; muscles 4 and 5 unite dorsally to form a common muscle A, which 

 crosses the middle line of the dorsal surface and becomes continuous with 

 its fellow of the opposite side. The muscle A has no equivalent in the 

 solitary form. Muscle 7 is continued ventrally into the organ of attach- 

 ment, where it unites with muscle 3 ; while muscle 7 unites dorsally with a 

 common muscle formed by the union of muscles 8 and 9, and thus gives 

 rise to the muscle B, which crosses the middle line of the dorsal surface to 

 become continuous with its fellow of the opposite side; muscles 6 and 8 

 unite with each other ventrally, and cross the middle line of the ventral sur- 

 face ; muscles 8 and 9 unite dorsally to form a common muscle, which is 

 joined by muscle 7 to form muscle B ; muscle C is a short oblique muscle 

 which joins muscle 10 to the muscle that is formed by the union of muscle 

 8 with muscle 9. 



