86 Papers from the Marine Biological Laboratory at Tortugas. 
Muscle 9 is nearly transverse dorsally, whereas its ventral half runs 
inwards and forwards. 
Muscle to is like muscle 9, except that its ventral half is still more in- 
clined forwards. 
Muscle 11 is like muscle 9 and muscle 10, except that its ventral half is 
still more inclined forwards. 
Muscle 12 crosses the middle line of the ventral surface, while its dorsal 
portions do not meet on the middle line. 
Muscles 11, 13, 14, and 15: I am not able to trace an exact homology 
between the muscles posterior to muscle 12 in the various species of Cyclo- 
salpa, although this failure may be due to a lack of detail in this region in 
the figures. 
Muscle 16, which occurs also in S. pinnata, is shown in S. floridana in 
figure 7, is a longitudinal muscle that connects muscle 1 with muscle 5. It 
is not visible in a symmetrical dorsal or ventral view, as it is on the side of 
the body, midway between the dorsal and the ventral surface. It is shown 
in the adult S. floridana on the left side of figure 1, which is not a perfectly 
dorsal view. 
The four known species of Cyclosalpa fall into two sets as regards the 
muscles of the solitary form. In Salpa pinnata and S. affinis the muscles 
are not united into groups or bundles, while they are so united in S. virgula, 
and S. floridana. 
In S. floridana (plate 1, figure 1) muscles 4, 5, and 7 of each side are 
united near the middle line of the dorsal surface into a single muscle, which 
does not cross the middle line nor unite with its fellow of the opposite side. 
In the ventral surface of the same species (figure 2) muscles 6, 7, 8, 9, and 10 
unite to form a common trunk, which crosses the middle line of the ventral 
surface to become continuous with its fellow of the opposite side. 
Since the muscles of the solitary cyclosalpas are homologous, and those 
of S. pinnata and S. affinis simple, or not united into groups, while those 
of S. floridana and S. virgula are more specialized, it seems natural to re- 
gard S. pinnata and S. affinis as more primitive. The study of the digestive 
organs corroborates this view and seems to indicate that all the cyclosalpas 
are derived from a pinnata-like ancestral form. 
In the solitary S. pinnata muscles 7, 8, 9, 10, and 11 are incomplete both 
dorsally and ventrally, and they are not joined into bundles. In S. affinis 
muscles 8, 9, 10, and 11 are complete dorsally, but not united into bundles. 
In S. floridana they are incomplete dorsally, but 4, 5, and 7 are united into 
a bundle on the dorsal surface, while muscles 6, 7, 8, 9, and 10 are com- 
plete ventrally and united into a bundle. 
