The Pelagic Tunicata of the Gulf Stream. 79 
colony is about half the size of that of S. pinnata. The one from which 
figure 9 was drawn is 12 mm. in diameter, and our largest specimens, with 
advanced embryos are about 20 mm. in diameter, which is, probably, near 
the maximum for S. floridana. The colony of S. pinnata from which plate 
2, figure 8, was drawn is 34 mm. in diameter, and the maximum is about 
40 mm. 
The members of the colony of S. floridana are joined together by slender 
processes, with lance-shaped ends which meet in the center in a star. The 
long axes of the animals are in the radii of the colony, while they are at 
right angles to it in S. pimnata. The animals are barrel-shaped, with their 
mouths central and their cloacal apertures distal—an arrangement that is 
the reverse of that of Pyrosoma, to which the colony presents a superficial 
resemblance. In the preserved specimen from which figure 9 was drawn, 
and in all my preserved specimens, the colony resembles a flat wheel, but 
in the living specimens the dorsal surface is slightly concave and the ven- 
tral surface slightly convex, these being features in common with S. pin- 
nata, as plate 2, figure 8, shows. In the living colony the long axes of the 
members of the community are slightly inclined, with the oral end a little 
nearer the central axis than the aboral end, so that the living colony is not 
as distinctly wheel-shaped as the preserved specimen from which figure 9 
was drawn. 
The muscular contractions of the aggregated S. floridana are vigorous, 
and the course of the gill differs according to the phase of muscular con- 
traction of the animal when it was killed. The animals shown in figures 
6 and 9 contracted as they were dropped into the killing fluid, and the gill 
is twisted into a right-hand spiral, which is constant in all the members of 
this community. The one that is shown in plate 1, figure 5, was killed with 
its muscles relaxed and its gill is straight, as it is in all the members of the 
colony from which this specimen was taken. Since neither phase of con- 
traction is any more normal than the other, the gill of the aggregated S. 
floridana must be characterized as straight when the muscles are relaxed, 
and spiral when they are contracted. 
THE DIGESTIVE ORGANS OF THE AGGREGATED SALPA FLORIDANA. 
The digestive organs of the aggregated S. floridana are very different 
from those of the solitary form, as Apstein points out. In the solitary form 
the intestine is long, straight, and it runs, inside the gill, from the ventral 
stomach to the dorsal anus, which is a little posterior to the ganglion. In 
the aggregated form (plate 1, figure 5) the intestine runs backwards, and, 
bending upon itself, runs dorsalwards to the anus, which is on the left side 
of its gastric end, as Apstein shows it in his figure 2, while he represents 
it on the right in his figure I. 
Apstein says the endostyle of the aggregated form extends in a straight 
