76 Papers from the Marine Biological Laboratory at Tortugas. 
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. 
CBlate igs! Pie) sen nlate 2 tien 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 1, figure I, is a dorsal view of the adult, magnified 16.5 
diameters. Plate 1, 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 1, figure 4, is a ventral view of an embryo at the stage that is described 
by Apstein, magnified 30 diameters. Plate 2, figure 7, is a side view of 
a younger embryo magnified I1oo 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 S. pinnata. It makes its appearance in the young embryo (plate 2, 
figure 7, Jum.) 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 1, figure 4) it occupies the intermuscular spaces 7-8, 8-9, and 
9-10, and even reaches beyond 8 and 10, as in plate 1, figures I and 2. It 
is in the body-cavity, and not in the muscles. 
The solitary S. floridana, from which plate 1, figures 1, 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. 
