76 Papers from the Marine Biological Laboratory at Tortngas. 



organ, for neither end of the muscle can be regarded as the origin. Ap- 

 stein's method of enumerating the muscles makes his account difficult to 

 follow with a specimen, and often leads him into inconsistency. Clearness 

 seems to demand that a muscle that is single on one surface and repre- 

 sented by two or more on the other surface should be described as several 

 muscles, and Apstein sometimes follows this rule, while upon other occasions 

 he departs from it. 



I have found it very difficult to make comparisons between the muscles 

 of different species without a more minute system of enumeration than the 

 diagnosis of species seems to require, and my chief reason for the method 

 that I here employ is to facilitate the description of homologies among the 

 muscles. 



THE SOLITARY SALPA FLORIDANA. 

 (Plate i. figs, i, 2, 3, 4; plate 2, fig. 7.) 



In the figures, the muscles that are on the surface of the body that is 

 nearest the observer are designated by Arabic numerals, while those that are 

 seen on the far side through the transparent body are designated by Roman 

 numerals. Plate i, figure i, is a dorsal view of the adult, magnified 16.5 

 diameters. Plate i, figure 2, is a ventral view of the same specimen. Plate 

 i, figure 3, shows the digestive organs of the same specimen in ventral view. 

 ' Plate i, figure 4, is a ventral view of an embryo at the stage that is described 

 by Apstein, magnified 30 diameters. Plate 2, figure /, is a side view of 

 a younger embryo magnified 100 diameters. 



On each side of the body of the solitary form there is an organ that 

 Apstein calls a glandular lateral organ. It is a luminous organ like those 

 of 5". pinnata. It makes its appearance in the young embryo (plate 2, 

 figure 7, luin.) in the plane of the muscle that is numbered 9 in my figures, 

 and it lengthens at each end as development progresses. In the older em- 

 bryos (plate i, figure 4) it occupies the intermuscular spaces 7-8, 8-9, and 

 9-10, and even reaches beyond 8 and 10, as in plate i, figures i and 2. It 

 is in the body-cavity, and not in the muscles. 



The solitary v$\ floridana, from which plate i, figures i, 2, and 3 were 

 drawn, is about 10 mm. long, and the average length is about 12 mm., as 

 Apstein says. The living animal is cylindrical, and Apstein is, no doubt, 

 right in attributing the flatness of his specimens to pressure against the 

 bottle in which they had been preserved. 



THE MUSCLES OF THE SOLITARY SALPA FLORIDANA. 



The homology between the muscles of S. floridana and those of the 

 other cyclosalpas is so exact that the equivalent of each muscle can be rec- 

 ognized in the other species without difficulty, and I shall give no detailed 

 account of them in this place, as the reader may refer to the general account 

 of the muscles of the cyclosalpas in Part III of this memoir. 



