“8 Papers from the Marine Biological Laboratory at Tortugas. 
tively thicker and more easy to trace, and the specimen shows clearly that 
muscles 13 and 14 are not united where they cross each other. The younger 
embryo that is shown, in side view, in plate 2, figure 7, shows the muscle 16 
that joins muscle 1 to muscle 5 on the side of the body. This muscle is 
difficult to see in a dorsal or ventral view. The left-hand one of the adult 
is shown, at 16, on the left side of figure 1 and the right-hand one is shown 
on the left side (right side inverted) of figure 2. 
Since the muscles of S. floridana are homologous with, but much more 
specialized than, those of S. pinnata, it seems natural to conclude that it is 
a modified descendant of an ancestral form that resembled S. pimnata, and 
this conclusion is strengthened by the comparative study of other organs. 
Apstein says that there is no other Salpa in which the muscles are 
joined to each other in as great a degree as they are in S. floridana, but a 
reference to Traustedt’s figure of S. hexagona will show that all the muscles 
are thus united in this species. (Traustedt, Spolia Atlantica, Tab. 1, fig. 14.) 
THE DIGESTIVE ORGANS AND STOLON OF THE SOLITARY SALPA FLORIDANA. 
(Plate 1, fig. 3.) 
The opening by which the pharynx communicates with the cesophagus 
is a large, funnel-shaped aperture, on the right side of the ventral end of 
the “gill.” It diminishes in size very rapidly, and opens into the anterior 
end of the stomach by an opening, c, which is very small as compared with 
the pharyngeal end. The stomach is joined, on the left, by a large blind 
pouch, the so-called liver. The aperture by which the stomach communi- 
cates with the intestine, 7, is at the junction of the blind pouch with the 
stomach. The intestine, 7, is long, and it runs upwards and forwards to 
open at the anus, a, into the median atrium or cloaca, near its dorsal surface 
and a little posterior to the ganglion. The intestine lies in that part of the 
body-cavity that is included in the so-called “ gill.” 
The stolon is twisted into a right-hand spiral, bending to the left from 
the fixed growing end of the median line and then bending to the right, 
so that the free end points to the right and is on the right of the middle 
line. In this respect the stolon of this species is very different from that 
of S. pinnata, and like that of ordinary salpas, such as S. democratica. 
THE AGGREGATED FORM OF SALPA FLORIDANA. 
(Plate 1, figs. 5 and 6; plate 2, fig. 9.) 
The colony of the aggregated form of S. floridana (plate 2, figure 9) is 
a circular rosette of four, five, or six or more individuals. In my collection 
there are some with four, some with five, and one with six, and none with 
more than six, although six may not be the maximum. The number is 
very much smaller than it is in other Cyclosalpas, as is shown by comparing 
figure 9 with the colony of S. pinnata shown in plate 2, figure 8. The 
